diff --git a/app/graphql/mutations/merge_requests/remove_attention_request.rb b/app/graphql/mutations/merge_requests/remove_attention_request.rb
new file mode 100644
index 0000000000000000000000000000000000000000..ab8617edb36ff2b468aa50dea0d0087ed8f67e37
--- /dev/null
+++ b/app/graphql/mutations/merge_requests/remove_attention_request.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Mutations
+  module MergeRequests
+    class RemoveAttentionRequest < Base
+      graphql_name 'MergeRequestRemoveAttentionRequest'
+
+      argument :user_id, ::Types::GlobalIDType[::User],
+               loads: Types::UserType,
+               required: true,
+               description: <<~DESC
+                            User ID of the user for attention request removal.
+               DESC
+
+      def resolve(project_path:, iid:, user:)
+        merge_request = authorized_find!(project_path: project_path, iid: iid)
+
+        result = ::MergeRequests::RemoveAttentionRequestedService.new(
+          project: merge_request.project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: user
+        ).execute
+
+        {
+          merge_request: merge_request,
+          errors: Array(result[:message])
+        }
+      end
+    end
+  end
+end
diff --git a/app/graphql/mutations/merge_requests/request_attention.rb b/app/graphql/mutations/merge_requests/request_attention.rb
new file mode 100644
index 0000000000000000000000000000000000000000..9a9f2f4cd435b656e9bb0a465819b8abd3586787
--- /dev/null
+++ b/app/graphql/mutations/merge_requests/request_attention.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Mutations
+  module MergeRequests
+    class RequestAttention < Base
+      graphql_name 'MergeRequestRequestAttention'
+
+      argument :user_id, ::Types::GlobalIDType[::User],
+               loads: Types::UserType,
+               required: true,
+               description: <<~DESC
+                            User ID of the user to request attention.
+               DESC
+
+      def resolve(project_path:, iid:, user:)
+        merge_request = authorized_find!(project_path: project_path, iid: iid)
+
+        result = ::MergeRequests::RequestAttentionService.new(
+          project: merge_request.project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: user
+        ).execute
+
+        {
+          merge_request: merge_request,
+          errors: Array(result[:message])
+        }
+      end
+    end
+  end
+end
diff --git a/app/graphql/types/mutation_type.rb b/app/graphql/types/mutation_type.rb
index 47d58e5dc60f9fa20cb44abcdc3016728b5abd7b..d6bfe6bf052dbd3a2b2783fae0511d1a0b015ee0 100644
--- a/app/graphql/types/mutation_type.rb
+++ b/app/graphql/types/mutation_type.rb
@@ -69,6 +69,8 @@ class MutationType < BaseObject
     mount_mutation Mutations::MergeRequests::SetDraft, calls_gitaly: true
     mount_mutation Mutations::MergeRequests::SetAssignees
     mount_mutation Mutations::MergeRequests::ReviewerRereview
+    mount_mutation Mutations::MergeRequests::RequestAttention, feature_flag: :mr_attention_requests
+    mount_mutation Mutations::MergeRequests::RemoveAttentionRequest, feature_flag: :mr_attention_requests
     mount_mutation Mutations::MergeRequests::ToggleAttentionRequested, feature_flag: :mr_attention_requests
     mount_mutation Mutations::Metrics::Dashboard::Annotations::Create
     mount_mutation Mutations::Metrics::Dashboard::Annotations::Delete
diff --git a/app/services/merge_requests/base_service.rb b/app/services/merge_requests/base_service.rb
index d197c13378ae43e27cb32fe621bcc8d3d8d829a6..8d06a1020c423c993f8d9e14c622b6d3596db782 100644
--- a/app/services/merge_requests/base_service.rb
+++ b/app/services/merge_requests/base_service.rb
@@ -256,7 +256,7 @@ def remove_all_attention_requests(merge_request)
     def remove_attention_requested(merge_request)
       return unless merge_request.attention_requested_enabled?
 
-      ::MergeRequests::RemoveAttentionRequestedService.new(project: merge_request.project, current_user: current_user, merge_request: merge_request).execute
+      ::MergeRequests::RemoveAttentionRequestedService.new(project: merge_request.project, current_user: current_user, merge_request: merge_request, user: current_user).execute
     end
   end
 end
diff --git a/app/services/merge_requests/remove_attention_requested_service.rb b/app/services/merge_requests/remove_attention_requested_service.rb
index a32a80714710cdd53f071c19288768b4596e001a..8a410fda69184c7c09408ced917918d7b6853e76 100644
--- a/app/services/merge_requests/remove_attention_requested_service.rb
+++ b/app/services/merge_requests/remove_attention_requested_service.rb
@@ -2,22 +2,26 @@
 
 module MergeRequests
   class RemoveAttentionRequestedService < MergeRequests::BaseService
-    attr_accessor :merge_request
+    attr_accessor :merge_request, :user
 
-    def initialize(project:, current_user:, merge_request:)
+    def initialize(project:, current_user:, merge_request:, user:)
       super(project: project, current_user: current_user)
 
       @merge_request = merge_request
+      @user = user
     end
 
     def execute
       return error("Invalid permissions") unless can?(current_user, :update_merge_request, merge_request)
 
       if reviewer || assignee
+        return success if reviewer&.reviewed? || assignee&.reviewed?
+
         update_state(reviewer)
         update_state(assignee)
 
-        current_user.invalidate_attention_requested_count
+        user.invalidate_attention_requested_count
+        create_remove_attention_request_note
 
         success
       else
@@ -28,15 +32,19 @@ def execute
     private
 
     def assignee
-      merge_request.find_assignee(current_user)
+      @assignee ||= merge_request.find_assignee(user)
     end
 
     def reviewer
-      merge_request.find_reviewer(current_user)
+      @reviewer ||= merge_request.find_reviewer(user)
     end
 
     def update_state(reviewer_or_assignee)
       reviewer_or_assignee&.update(state: :reviewed)
     end
+
+    def create_remove_attention_request_note
+      SystemNoteService.remove_attention_request(merge_request, merge_request.project, current_user, user)
+    end
   end
 end
diff --git a/app/services/merge_requests/request_attention_service.rb b/app/services/merge_requests/request_attention_service.rb
new file mode 100644
index 0000000000000000000000000000000000000000..07e9996f87b134bdbb9e10482b94faf36bc11602
--- /dev/null
+++ b/app/services/merge_requests/request_attention_service.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+module MergeRequests
+  class RequestAttentionService < MergeRequests::BaseService
+    attr_accessor :merge_request, :user
+
+    def initialize(project:, current_user:, merge_request:, user:)
+      super(project: project, current_user: current_user)
+
+      @merge_request = merge_request
+      @user = user
+    end
+
+    def execute
+      return error("Invalid permissions") unless can?(current_user, :update_merge_request, merge_request)
+
+      if reviewer || assignee
+        return success if reviewer&.attention_requested? || assignee&.attention_requested?
+
+        update_state(reviewer)
+        update_state(assignee)
+
+        user.invalidate_attention_requested_count
+        create_attention_request_note
+        notity_user
+
+        if current_user.id != user.id
+          remove_attention_requested(merge_request)
+        end
+
+        success
+      else
+        error("User is not a reviewer or assignee of the merge request")
+      end
+    end
+
+    private
+
+    def notity_user
+      notification_service.async.attention_requested_of_merge_request(merge_request, current_user, user)
+      todo_service.create_attention_requested_todo(merge_request, current_user, user)
+    end
+
+    def create_attention_request_note
+      SystemNoteService.request_attention(merge_request, merge_request.project, current_user, user)
+    end
+
+    def assignee
+      @assignee ||= merge_request.find_assignee(user)
+    end
+
+    def reviewer
+      @reviewer ||= merge_request.find_reviewer(user)
+    end
+
+    def update_state(reviewer_or_assignee)
+      reviewer_or_assignee&.update(state: :attention_requested, updated_state_by: current_user)
+    end
+  end
+end
diff --git a/doc/api/graphql/reference/index.md b/doc/api/graphql/reference/index.md
index b88e52456c1f4a01b3372ab43d2b0cb11ad6a0cf..34e1e6f73972775b4ca919bf4f5e24d11d8ae28d 100644
--- a/doc/api/graphql/reference/index.md
+++ b/doc/api/graphql/reference/index.md
@@ -3459,6 +3459,52 @@ Input type: `MergeRequestCreateInput`
 | <a id="mutationmergerequestcreateerrors"></a>`errors` | [`[String!]!`](#string) | Errors encountered during execution of the mutation. |
 | <a id="mutationmergerequestcreatemergerequest"></a>`mergeRequest` | [`MergeRequest`](#mergerequest) | Merge request after mutation. |
 
+### `Mutation.mergeRequestRemoveAttentionRequest`
+
+Available only when feature flag `mr_attention_requests` is enabled. This flag is disabled by default, because the feature is experimental and is subject to change without notice.
+
+Input type: `MergeRequestRemoveAttentionRequestInput`
+
+#### Arguments
+
+| Name | Type | Description |
+| ---- | ---- | ----------- |
+| <a id="mutationmergerequestremoveattentionrequestclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
+| <a id="mutationmergerequestremoveattentionrequestiid"></a>`iid` | [`String!`](#string) | IID of the merge request to mutate. |
+| <a id="mutationmergerequestremoveattentionrequestprojectpath"></a>`projectPath` | [`ID!`](#id) | Project the merge request to mutate is in. |
+| <a id="mutationmergerequestremoveattentionrequestuserid"></a>`userId` | [`UserID!`](#userid) | User ID of the user for attention request removal. |
+
+#### Fields
+
+| Name | Type | Description |
+| ---- | ---- | ----------- |
+| <a id="mutationmergerequestremoveattentionrequestclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
+| <a id="mutationmergerequestremoveattentionrequesterrors"></a>`errors` | [`[String!]!`](#string) | Errors encountered during execution of the mutation. |
+| <a id="mutationmergerequestremoveattentionrequestmergerequest"></a>`mergeRequest` | [`MergeRequest`](#mergerequest) | Merge request after mutation. |
+
+### `Mutation.mergeRequestRequestAttention`
+
+Available only when feature flag `mr_attention_requests` is enabled. This flag is disabled by default, because the feature is experimental and is subject to change without notice.
+
+Input type: `MergeRequestRequestAttentionInput`
+
+#### Arguments
+
+| Name | Type | Description |
+| ---- | ---- | ----------- |
+| <a id="mutationmergerequestrequestattentionclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
+| <a id="mutationmergerequestrequestattentioniid"></a>`iid` | [`String!`](#string) | IID of the merge request to mutate. |
+| <a id="mutationmergerequestrequestattentionprojectpath"></a>`projectPath` | [`ID!`](#id) | Project the merge request to mutate is in. |
+| <a id="mutationmergerequestrequestattentionuserid"></a>`userId` | [`UserID!`](#userid) | User ID of the user to request attention. |
+
+#### Fields
+
+| Name | Type | Description |
+| ---- | ---- | ----------- |
+| <a id="mutationmergerequestrequestattentionclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
+| <a id="mutationmergerequestrequestattentionerrors"></a>`errors` | [`[String!]!`](#string) | Errors encountered during execution of the mutation. |
+| <a id="mutationmergerequestrequestattentionmergerequest"></a>`mergeRequest` | [`MergeRequest`](#mergerequest) | Merge request after mutation. |
+
 ### `Mutation.mergeRequestReviewerRereview`
 
 Input type: `MergeRequestReviewerRereviewInput`
diff --git a/spec/requests/api/graphql/mutations/merge_requests/request_attention_spec.rb b/spec/requests/api/graphql/mutations/merge_requests/request_attention_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..e96f8ce55395d775493d1e243d132aa739a58ec7
--- /dev/null
+++ b/spec/requests/api/graphql/mutations/merge_requests/request_attention_spec.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Request attention' do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:merge_request) { create(:merge_request, reviewers: [user]) }
+  let_it_be(:project) { merge_request.project }
+
+  let(:input) { { user_id: global_id_of(user) } }
+
+  let(:mutation) do
+    variables = {
+      project_path: project.full_path,
+      iid: merge_request.iid.to_s
+    }
+    graphql_mutation(:merge_request_request_attention, variables.merge(input),
+                     <<-QL.strip_heredoc
+                       clientMutationId
+                       errors
+    QL
+    )
+  end
+
+  def mutation_response
+    graphql_mutation_response(:merge_request_request_attention)
+  end
+
+  def mutation_errors
+    mutation_response['errors']
+  end
+
+  before_all do
+    project.add_developer(current_user)
+    project.add_developer(user)
+  end
+
+  it 'is successful' do
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_errors).to be_empty
+  end
+
+  context 'when current user is not allowed to update the merge request' do
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: create(:user))
+
+      expect(graphql_errors).not_to be_empty
+    end
+  end
+
+  context 'when user is not a reviewer' do
+    let(:input) { { user_id: global_id_of(create(:user)) } }
+
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_errors).not_to be_empty
+    end
+  end
+end
diff --git a/spec/requests/api/graphql/mutations/remove_attention_request_spec.rb b/spec/requests/api/graphql/mutations/remove_attention_request_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..0a7ced1a30ce18946748d366aad1bda87fe94bb4
--- /dev/null
+++ b/spec/requests/api/graphql/mutations/remove_attention_request_spec.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Remove attention request' do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:merge_request) { create(:merge_request, reviewers: [user]) }
+  let_it_be(:project) { merge_request.project }
+
+  let(:input) { { user_id: global_id_of(user) } }
+
+  let(:mutation) do
+    variables = {
+      project_path: project.full_path,
+      iid: merge_request.iid.to_s
+    }
+    graphql_mutation(:merge_request_remove_attention_request, variables.merge(input),
+                     <<-QL.strip_heredoc
+                       clientMutationId
+                       errors
+    QL
+    )
+  end
+
+  def mutation_response
+    graphql_mutation_response(:merge_request_remove_attention_request)
+  end
+
+  def mutation_errors
+    mutation_response['errors']
+  end
+
+  before_all do
+    project.add_developer(current_user)
+    project.add_developer(user)
+  end
+
+  it 'is successful' do
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_errors).to be_empty
+  end
+
+  context 'when current user is not allowed to update the merge request' do
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: create(:user))
+
+      expect(graphql_errors).not_to be_empty
+    end
+  end
+
+  context 'when user is not a reviewer' do
+    let(:input) { { user_id: global_id_of(create(:user)) } }
+
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_errors).not_to be_empty
+    end
+  end
+end
diff --git a/spec/services/merge_requests/approval_service_spec.rb b/spec/services/merge_requests/approval_service_spec.rb
index 9b064da44b845f2f798d57b73c24821b121c986b..4d20d62b864403d01be17712d7e1ce948428dbf8 100644
--- a/spec/services/merge_requests/approval_service_spec.rb
+++ b/spec/services/merge_requests/approval_service_spec.rb
@@ -61,7 +61,7 @@
 
       it 'removes attention requested state' do
         expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
-          .with(project: project, current_user: user, merge_request: merge_request)
+          .with(project: project, current_user: user, merge_request: merge_request, user: user)
           .and_call_original
 
         service.execute(merge_request)
diff --git a/spec/services/merge_requests/handle_assignees_change_service_spec.rb b/spec/services/merge_requests/handle_assignees_change_service_spec.rb
index 26f53f55b0fcfd59ee8438ff956346a7b7b4b7af..34c598e6cc0830117e72445b1848e1283c71bc63 100644
--- a/spec/services/merge_requests/handle_assignees_change_service_spec.rb
+++ b/spec/services/merge_requests/handle_assignees_change_service_spec.rb
@@ -89,7 +89,7 @@ def execute
 
     it 'removes attention requested state' do
       expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
-        .with(project: project, current_user: user, merge_request: merge_request)
+        .with(project: project, current_user: user, merge_request: merge_request, user: user)
         .and_call_original
 
       execute
diff --git a/spec/services/merge_requests/remove_attention_requested_service_spec.rb b/spec/services/merge_requests/remove_attention_requested_service_spec.rb
index 450204ebfdde988fb5cc3236ff474974361b3ba8..576049b9f1b58ce3ef4cd661af7259f393580348 100644
--- a/spec/services/merge_requests/remove_attention_requested_service_spec.rb
+++ b/spec/services/merge_requests/remove_attention_requested_service_spec.rb
@@ -3,64 +3,112 @@
 require 'spec_helper'
 
 RSpec.describe MergeRequests::RemoveAttentionRequestedService do
-  let(:current_user) { create(:user) }
-  let(:merge_request) { create(:merge_request, reviewers: [current_user], assignees: [current_user]) }
-  let(:reviewer) { merge_request.find_reviewer(current_user) }
-  let(:assignee) { merge_request.find_assignee(current_user) }
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:assignee_user) { create(:user) }
+  let_it_be(:merge_request) { create(:merge_request, reviewers: [user], assignees: [assignee_user]) }
+
+  let(:reviewer) { merge_request.find_reviewer(user) }
+  let(:assignee) { merge_request.find_assignee(assignee_user) }
   let(:project) { merge_request.project }
-  let(:service) { described_class.new(project: project, current_user: current_user, merge_request: merge_request) }
+
+  let(:service) do
+    described_class.new(
+      project: project,
+      current_user: current_user,
+      merge_request: merge_request,
+      user: user
+    )
+  end
+
   let(:result) { service.execute }
 
   before do
+    allow(SystemNoteService).to receive(:remove_attention_request)
+
     project.add_developer(current_user)
+    project.add_developer(user)
   end
 
   describe '#execute' do
-    context 'invalid permissions' do
-      let(:service) { described_class.new(project: project, current_user: create(:user), merge_request: merge_request) }
+    context 'when current user cannot update merge request' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: create(:user),
+          merge_request: merge_request,
+          user: user
+        )
+      end
 
       it 'returns an error' do
         expect(result[:status]).to eq :error
       end
     end
 
-    context 'reviewer does not exist' do
-      let(:service) { described_class.new(project: project, current_user: create(:user), merge_request: merge_request) }
+    context 'when user is not a reviewer nor assignee' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: create(:user)
+        )
+      end
 
       it 'returns an error' do
         expect(result[:status]).to eq :error
       end
     end
 
-    context 'reviewer exists' do
+    context 'when user is a reviewer' do
+      before do
+        reviewer.update!(state: :attention_requested)
+      end
+
       it 'returns success' do
         expect(result[:status]).to eq :success
       end
 
-      it 'updates reviewers state' do
+      it 'updates reviewer state' do
         service.execute
         reviewer.reload
 
         expect(reviewer.state).to eq 'reviewed'
       end
 
+      it 'creates a remove attention request system note' do
+        expect(SystemNoteService)
+          .to receive(:remove_attention_request)
+          .with(merge_request, merge_request.project, current_user, user)
+
+        service.execute
+      end
+
       it_behaves_like 'invalidates attention request cache' do
-        let(:users) { [current_user] }
+        let(:users) { [user] }
       end
     end
 
-    context 'assignee exists' do
-      let(:service) { described_class.new(project: project, current_user: current_user, merge_request: merge_request) }
+    context 'when user is an assignee' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: assignee_user
+        )
+      end
 
       before do
-        assignee.update!(state: :reviewed)
+        assignee.update!(state: :attention_requested)
       end
 
       it 'returns success' do
         expect(result[:status]).to eq :success
       end
 
-      it 'updates assignees state' do
+      it 'updates assignee state' do
         service.execute
         assignee.reload
 
@@ -68,14 +116,40 @@
       end
 
       it_behaves_like 'invalidates attention request cache' do
-        let(:users) { [current_user] }
+        let(:users) { [assignee_user] }
+      end
+
+      it 'creates a remove attention request system note' do
+        expect(SystemNoteService)
+          .to receive(:remove_attention_request)
+          .with(merge_request, merge_request.project, current_user, assignee_user)
+
+        service.execute
       end
     end
 
-    context 'assignee is the same as reviewer' do
-      let(:merge_request) { create(:merge_request, reviewers: [current_user], assignees: [current_user]) }
-      let(:service) { described_class.new(project: project, current_user: current_user, merge_request: merge_request) }
-      let(:assignee) { merge_request.find_assignee(current_user) }
+    context 'when user is an assignee and reviewer at the same time' do
+      let_it_be(:merge_request) { create(:merge_request, reviewers: [user], assignees: [user]) }
+
+      let(:assignee) { merge_request.find_assignee(user) }
+
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: user
+        )
+      end
+
+      before do
+        reviewer.update!(state: :attention_requested)
+        assignee.update!(state: :attention_requested)
+      end
+
+      it 'returns success' do
+        expect(result[:status]).to eq :success
+      end
 
       it 'updates reviewers and assignees state' do
         service.execute
@@ -86,5 +160,24 @@
         expect(assignee.state).to eq 'reviewed'
       end
     end
+
+    context 'when state is already not attention_requested' do
+      before do
+        reviewer.update!(state: :reviewed)
+      end
+
+      it 'does not change state' do
+        service.execute
+        reviewer.reload
+
+        expect(reviewer.state).to eq 'reviewed'
+      end
+
+      it 'does not create a remove attention request system note' do
+        expect(SystemNoteService).not_to receive(:remove_attention_request)
+
+        service.execute
+      end
+    end
   end
 end
diff --git a/spec/services/merge_requests/request_attention_service_spec.rb b/spec/services/merge_requests/request_attention_service_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..813a8150625c90c76ac7aa301f95712dbeedc34a
--- /dev/null
+++ b/spec/services/merge_requests/request_attention_service_spec.rb
@@ -0,0 +1,220 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe MergeRequests::RequestAttentionService do
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:assignee_user) { create(:user) }
+  let_it_be(:merge_request) { create(:merge_request, reviewers: [user], assignees: [assignee_user]) }
+
+  let(:reviewer) { merge_request.find_reviewer(user) }
+  let(:assignee) { merge_request.find_assignee(assignee_user) }
+  let(:project) { merge_request.project }
+
+  let(:service) do
+    described_class.new(
+      project: project,
+      current_user: current_user,
+      merge_request: merge_request,
+      user: user
+    )
+  end
+
+  let(:result) { service.execute }
+  let(:todo_svc) { instance_double('TodoService') }
+  let(:notification_svc) { instance_double('NotificationService') }
+
+  before do
+    allow(service).to receive(:todo_service).and_return(todo_svc)
+    allow(service).to receive(:notification_service).and_return(notification_svc)
+    allow(todo_svc).to receive(:create_attention_requested_todo)
+    allow(notification_svc).to receive_message_chain(:async, :attention_requested_of_merge_request)
+    allow(SystemNoteService).to receive(:request_attention)
+
+    project.add_developer(current_user)
+    project.add_developer(user)
+  end
+
+  describe '#execute' do
+    context 'when current user cannot update merge request' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: create(:user),
+          merge_request: merge_request,
+          user: user
+        )
+      end
+
+      it 'returns an error' do
+        expect(result[:status]).to eq :error
+      end
+    end
+
+    context 'when user is not a reviewer nor assignee' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: create(:user)
+        )
+      end
+
+      it 'returns an error' do
+        expect(result[:status]).to eq :error
+      end
+    end
+
+    context 'when user is a reviewer' do
+      before do
+        reviewer.update!(state: :reviewed)
+      end
+
+      it 'returns success' do
+        expect(result[:status]).to eq :success
+      end
+
+      it 'updates reviewers state' do
+        service.execute
+        reviewer.reload
+
+        expect(reviewer.state).to eq 'attention_requested'
+      end
+
+      it 'adds who toggled attention' do
+        service.execute
+        reviewer.reload
+
+        expect(reviewer.updated_state_by).to eq current_user
+      end
+
+      it 'creates a new todo for the reviewer' do
+        expect(todo_svc).to receive(:create_attention_requested_todo).with(merge_request, current_user, user)
+
+        service.execute
+      end
+
+      it 'sends email to reviewer' do
+        expect(notification_svc)
+          .to receive_message_chain(:async, :attention_requested_of_merge_request)
+          .with(merge_request, current_user, user)
+
+        service.execute
+      end
+
+      it 'removes attention requested state' do
+        expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
+          .with(project: project, current_user: current_user, merge_request: merge_request, user: current_user)
+          .and_call_original
+
+        service.execute
+      end
+
+      it_behaves_like 'invalidates attention request cache' do
+        let(:users) { [user] }
+      end
+    end
+
+    context 'when user is an assignee' do
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: assignee_user
+        )
+      end
+
+      before do
+        assignee.update!(state: :reviewed)
+      end
+
+      it 'returns success' do
+        expect(result[:status]).to eq :success
+      end
+
+      it 'updates assignees state' do
+        service.execute
+        assignee.reload
+
+        expect(assignee.state).to eq 'attention_requested'
+      end
+
+      it 'creates a new todo for the reviewer' do
+        expect(todo_svc).to receive(:create_attention_requested_todo).with(merge_request, current_user, assignee_user)
+
+        service.execute
+      end
+
+      it 'creates a request attention system note' do
+        expect(SystemNoteService)
+          .to receive(:request_attention)
+          .with(merge_request, merge_request.project, current_user, assignee_user)
+
+        service.execute
+      end
+
+      it 'removes attention requested state' do
+        expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
+          .with(project: project, current_user: current_user, merge_request: merge_request, user: current_user)
+          .and_call_original
+
+        service.execute
+      end
+
+      it_behaves_like 'invalidates attention request cache' do
+        let(:users) { [assignee_user] }
+      end
+    end
+
+    context 'when user is an assignee and reviewer at the same time' do
+      let_it_be(:merge_request) { create(:merge_request, reviewers: [user], assignees: [user]) }
+
+      let(:assignee) { merge_request.find_assignee(user) }
+
+      let(:service) do
+        described_class.new(
+          project: project,
+          current_user: current_user,
+          merge_request: merge_request,
+          user: user
+        )
+      end
+
+      before do
+        reviewer.update!(state: :reviewed)
+        assignee.update!(state: :reviewed)
+      end
+
+      it 'updates reviewers and assignees state' do
+        service.execute
+        reviewer.reload
+        assignee.reload
+
+        expect(reviewer.state).to eq 'attention_requested'
+        expect(assignee.state).to eq 'attention_requested'
+      end
+    end
+
+    context 'when state is attention_requested' do
+      before do
+        reviewer.update!(state: :attention_requested)
+      end
+
+      it 'does not change state' do
+        service.execute
+        reviewer.reload
+
+        expect(reviewer.state).to eq 'attention_requested'
+      end
+
+      it 'does not create a new todo for the reviewer' do
+        expect(todo_svc).not_to receive(:create_attention_requested_todo).with(merge_request, current_user, user)
+
+        service.execute
+      end
+    end
+  end
+end
diff --git a/spec/services/merge_requests/toggle_attention_requested_service_spec.rb b/spec/services/merge_requests/toggle_attention_requested_service_spec.rb
index dcaac5d26996a4f2f29436dc7d98c37071938e10..20bc536b21e7c18483a65991d93cab7925703ec6 100644
--- a/spec/services/merge_requests/toggle_attention_requested_service_spec.rb
+++ b/spec/services/merge_requests/toggle_attention_requested_service_spec.rb
@@ -80,7 +80,7 @@
 
       it 'removes attention requested state' do
         expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
-          .with(project: project, current_user: current_user, merge_request: merge_request)
+          .with(project: project, current_user: current_user, merge_request: merge_request, user: current_user)
           .and_call_original
 
         service.execute
@@ -129,7 +129,7 @@
 
       it 'removes attention requested state' do
         expect(MergeRequests::RemoveAttentionRequestedService).to receive(:new)
-          .with(project: project, current_user: current_user, merge_request: merge_request)
+          .with(project: project, current_user: current_user, merge_request: merge_request, user: current_user)
           .and_call_original
 
         service.execute