diff --git a/src/Core/AdminConsole/Services/Implementations/OrganizationService.cs b/src/Core/AdminConsole/Services/Implementations/OrganizationService.cs
index 6850ab013..43890919e 100644
--- a/src/Core/AdminConsole/Services/Implementations/OrganizationService.cs
+++ b/src/Core/AdminConsole/Services/Implementations/OrganizationService.cs
@@ -64,6 +64,8 @@ public class OrganizationService : IOrganizationService
     private readonly IDataProtectorTokenFactory<OrgUserInviteTokenable> _orgUserInviteTokenDataFactory;
     private readonly IFeatureService _featureService;
 
+    private bool FlexibleCollectionsIsEnabled => _featureService.IsEnabled(FeatureFlagKeys.FlexibleCollections, _currentContext);
+
     public OrganizationService(
         IOrganizationRepository organizationRepository,
         IOrganizationUserRepository organizationUserRepository,
@@ -1968,6 +1970,11 @@ public class OrganizationService : IOrganizationService
         {
             throw new BadRequestException("Custom users can only grant the same custom permissions that they have.");
         }
+
+        if (FlexibleCollectionsIsEnabled && newType == OrganizationUserType.Manager && oldType is not OrganizationUserType.Manager)
+        {
+            throw new BadRequestException("Manager role is deprecated after Flexible Collections.");
+        }
     }
 
     private async Task ValidateOrganizationCustomPermissionsEnabledAsync(Guid organizationId, OrganizationUserType newType)
diff --git a/src/Core/Context/CurrentContext.cs b/src/Core/Context/CurrentContext.cs
index ea0235ca2..478edda0d 100644
--- a/src/Core/Context/CurrentContext.cs
+++ b/src/Core/Context/CurrentContext.cs
@@ -283,6 +283,11 @@ public class CurrentContext : ICurrentContext
 
     public async Task<bool> OrganizationManager(Guid orgId)
     {
+        if (FlexibleCollectionsIsEnabled)
+        {
+            throw new FeatureUnavailableException("Flexible Collections is ON when it should be OFF.");
+        }
+
         return await OrganizationAdmin(orgId) ||
                (Organizations?.Any(o => o.Id == orgId && o.Type == OrganizationUserType.Manager) ?? false);
     }
diff --git a/src/Core/Context/ICurrentContext.cs b/src/Core/Context/ICurrentContext.cs
index 2d3990f32..57fa7271b 100644
--- a/src/Core/Context/ICurrentContext.cs
+++ b/src/Core/Context/ICurrentContext.cs
@@ -36,6 +36,7 @@ public interface ICurrentContext
 
 
     Task<bool> OrganizationUser(Guid orgId);
+    [Obsolete("Manager role is deprecated after Flexible Collections.")]
     Task<bool> OrganizationManager(Guid orgId);
     Task<bool> OrganizationAdmin(Guid orgId);
     Task<bool> OrganizationOwner(Guid orgId);
diff --git a/test/Core.Test/AdminConsole/Services/OrganizationServiceTests.cs b/test/Core.Test/AdminConsole/Services/OrganizationServiceTests.cs
index 147ecac1c..00a94efed 100644
--- a/test/Core.Test/AdminConsole/Services/OrganizationServiceTests.cs
+++ b/test/Core.Test/AdminConsole/Services/OrganizationServiceTests.cs
@@ -826,6 +826,26 @@ public class OrganizationServiceTests
         });
     }
 
+    [Theory, BitAutoData]
+    public async Task InviteUser_WithFCEnabled_WhenInvitingManager_Throws(Organization organization, OrganizationUserInvite invite,
+        OrganizationUser invitor, SutProvider<OrganizationService> sutProvider)
+    {
+        invite.Type = OrganizationUserType.Manager;
+
+        sutProvider.GetDependency<IFeatureService>()
+            .IsEnabled(FeatureFlagKeys.FlexibleCollections, Arg.Any<ICurrentContext>())
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .ManageUsers(organization.Id)
+            .Returns(true);
+
+        var exception = await Assert.ThrowsAsync<BadRequestException>(
+            () => sutProvider.Sut.InviteUsersAsync(organization.Id, invitor.UserId, new (OrganizationUserInvite, string)[] { (invite, null) }));
+
+        Assert.Contains("manager role is deprecated", exception.Message.ToLowerInvariant());
+    }
+
     private void InviteUserHelper_ArrangeValidPermissions(Organization organization, OrganizationUser savingUser,
     SutProvider<OrganizationService> sutProvider)
     {
@@ -1106,6 +1126,38 @@ public class OrganizationServiceTests
         Assert.Contains("custom users can not manage admins or owners", exception.Message.ToLowerInvariant());
     }
 
+    [Theory, BitAutoData]
+    public async Task SaveUser_WithFCEnabled_WhenUpgradingToManager_Throws(
+        Organization organization,
+        [OrganizationUser(type: OrganizationUserType.User)] OrganizationUser oldUserData,
+        [OrganizationUser(type: OrganizationUserType.Manager)] OrganizationUser newUserData,
+        IEnumerable<CollectionAccessSelection> collections,
+        IEnumerable<Guid> groups,
+        SutProvider<OrganizationService> sutProvider)
+    {
+        sutProvider.GetDependency<IFeatureService>()
+            .IsEnabled(FeatureFlagKeys.FlexibleCollections, Arg.Any<ICurrentContext>())
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .ManageUsers(organization.Id)
+            .Returns(true);
+
+        sutProvider.GetDependency<IOrganizationUserRepository>()
+            .GetByIdAsync(oldUserData.Id)
+            .Returns(oldUserData);
+
+        newUserData.Id = oldUserData.Id;
+        newUserData.UserId = oldUserData.UserId;
+        newUserData.OrganizationId = oldUserData.OrganizationId = organization.Id;
+        newUserData.Permissions = CoreHelpers.ClassToJsonData(new Permissions());
+
+        var exception = await Assert.ThrowsAsync<BadRequestException>(
+            () => sutProvider.Sut.SaveUserAsync(newUserData, oldUserData.UserId, collections, groups));
+
+        Assert.Contains("manager role is deprecated", exception.Message.ToLowerInvariant());
+    }
+
     [Theory, BitAutoData]
     public async Task DeleteUser_InvalidUser(OrganizationUser organizationUser, OrganizationUser deletingUser,
         SutProvider<OrganizationService> sutProvider)