diff --git a/app/models/integrations/base_chat_notification.rb b/app/models/integrations/base_chat_notification.rb
index fa5ce098379c48a939ac42260c24b77cf37ed019..963ba918089024c7a63c2594274c203aa44e94af 100644
--- a/app/models/integrations/base_chat_notification.rb
+++ b/app/models/integrations/base_chat_notification.rb
@@ -23,6 +23,7 @@ class BaseChatNotification < Integration
     ].freeze
 
     SECRET_MASK = '************'
+    CHANNEL_LIMIT_PER_EVENT = 10
 
     attribute :category, default: 'chat'
 
@@ -37,7 +38,8 @@ class BaseChatNotification < Integration
               presence: true,
               public_url: true,
               if: -> (integration) { integration.activated? && integration.requires_webhook? }
-    validates :labels_to_be_notified_behavior, inclusion: { in: LABEL_NOTIFICATION_BEHAVIOURS }, allow_blank: true
+    validates :labels_to_be_notified_behavior, inclusion: { in: LABEL_NOTIFICATION_BEHAVIOURS }, allow_blank: true, if: :activated?
+    validate :validate_channel_limit, if: :activated?
 
     def initialize_properties
       super
@@ -300,7 +302,7 @@ def channels_for_event(event)
       channel_names = event_channel_value(event).presence || channel.presence
       return [] unless channel_names
 
-      channel_names.split(',').map(&:strip)
+      channel_names.split(',').map(&:strip).uniq
     end
 
     def unique_channels
@@ -308,6 +310,21 @@ def unique_channels
         channels_for_event(event)
       end.uniq
     end
+
+    def validate_channel_limit
+      supported_events.each do |event|
+        count = channels_for_event(event).count
+        next unless count > CHANNEL_LIMIT_PER_EVENT
+
+        errors.add(
+          event_channel_name(event).to_sym,
+          format(
+            s_('SlackIntegration|cannot have more than %{limit} channels'),
+            limit: CHANNEL_LIMIT_PER_EVENT
+          )
+        )
+      end
+    end
   end
 end
 
diff --git a/doc/user/project/integrations/mattermost.md b/doc/user/project/integrations/mattermost.md
index 39b89cd87a9946763f42284978490a9cfac69dc3..3782d3acd0cb35f7300d40280452d6630c9d45ce 100644
--- a/doc/user/project/integrations/mattermost.md
+++ b/doc/user/project/integrations/mattermost.md
@@ -36,6 +36,8 @@ Display name override is not enabled by default, you need to ask your administra
 
 ## Configure GitLab to send notifications to Mattermost
 
+> [Changed](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/106760) in GitLab 15.9 to limit Mattermost channels to 10 per event.
+
 After the Mattermost instance has an incoming webhook set up, you can set up GitLab
 to send the notifications:
 
diff --git a/doc/user/project/integrations/slack.md b/doc/user/project/integrations/slack.md
index 9932e782ff41b5937ef51da0e1d228d1bfadb5d6..d14401a5c9dedcd923501fd9608e168fede15cbb 100644
--- a/doc/user/project/integrations/slack.md
+++ b/doc/user/project/integrations/slack.md
@@ -28,6 +28,8 @@ to control GitLab from Slack. Slash commands are configured separately.
 
 ## Configure GitLab
 
+> [Changed](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/106760) in GitLab 15.9 to limit Slack channels to 10 per event.
+
 1. On the top bar, select **Main menu > Projects** and find your project.
 1. On the left sidebar, select **Settings > Integrations**.
 1. Select **Slack notifications**.
diff --git a/locale/gitlab.pot b/locale/gitlab.pot
index 13ae7fc419eeaf701f132be16acd3564277e22c7..570e19285621ee35b5da2028c82e71fe2a0d96ef 100644
--- a/locale/gitlab.pot
+++ b/locale/gitlab.pot
@@ -40071,6 +40071,9 @@ msgstr ""
 msgid "SlackIntegration|You may need to reinstall the GitLab for Slack app when we %{linkStart}make updates or change permissions%{linkEnd}."
 msgstr ""
 
+msgid "SlackIntegration|cannot have more than %{limit} channels"
+msgstr ""
+
 msgid "SlackModal|Are you sure you want to change the project?"
 msgstr ""
 
diff --git a/spec/models/integrations/base_chat_notification_spec.rb b/spec/models/integrations/base_chat_notification_spec.rb
index 1527ffd727839587977472e7f441dc420d074178..13dd9e03ab118238ee4535e48b7fa8e5d54e597d 100644
--- a/spec/models/integrations/base_chat_notification_spec.rb
+++ b/spec/models/integrations/base_chat_notification_spec.rb
@@ -9,13 +9,33 @@
 
   describe 'validations' do
     before do
-      allow(subject).to receive(:activated?).and_return(true)
+      subject.active = active
+
       allow(subject).to receive(:default_channel_placeholder).and_return('placeholder')
       allow(subject).to receive(:webhook_help).and_return('help')
     end
 
-    it { is_expected.to validate_presence_of :webhook }
-    it { is_expected.to validate_inclusion_of(:labels_to_be_notified_behavior).in_array(%w[match_any match_all]).allow_blank }
+    def build_channel_list(count)
+      (1..count).map { |i| "##{i}" }.join(',')
+    end
+
+    context 'when active' do
+      let(:active) { true }
+
+      it { is_expected.to validate_presence_of :webhook }
+      it { is_expected.to validate_inclusion_of(:labels_to_be_notified_behavior).in_array(%w[match_any match_all]).allow_blank }
+      it { is_expected.to allow_value(build_channel_list(10)).for(:push_channel) }
+      it { is_expected.not_to allow_value(build_channel_list(11)).for(:push_channel) }
+    end
+
+    context 'when inactive' do
+      let(:active) { false }
+
+      it { is_expected.not_to validate_presence_of :webhook }
+      it { is_expected.not_to validate_inclusion_of(:labels_to_be_notified_behavior).in_array(%w[match_any match_all]).allow_blank }
+      it { is_expected.to allow_value(build_channel_list(10)).for(:push_channel) }
+      it { is_expected.to allow_value(build_channel_list(11)).for(:push_channel) }
+    end
   end
 
   describe '#execute' do
@@ -309,6 +329,10 @@
     context 'with multiple channel names with spaces specified' do
       it_behaves_like 'with channel specified', 'slack-integration, #slack-test, @UDLP91W0A', ['slack-integration', '#slack-test', '@UDLP91W0A']
     end
+
+    context 'with duplicate channel names' do
+      it_behaves_like 'with channel specified', '#slack-test,#slack-test,#slack-test-2', ['#slack-test', '#slack-test-2']
+    end
   end
 
   describe '#default_channel_placeholder' do