diff --git a/lib/tasks/data_hygiene.rake b/lib/tasks/data_hygiene.rake
index 4402dfb8d..0e4bd8a63 100644
--- a/lib/tasks/data_hygiene.rake
+++ b/lib/tasks/data_hygiene.rake
@@ -12,4 +12,15 @@ namespace :data_hygiene do
     organisation.update!(closed: true)
     puts "Marked organisation #{organisation.slug} as closed"
   end
+
+  desc "Move all users from one organisation to another"
+  task :bulk_update_user_organisation, %i[old_content_id new_content_id] => :environment do |_, args|
+    old_organisation = Organisation.find_by(content_id: args[:old_content_id])
+    new_organisation = Organisation.find_by(content_id: args[:new_content_id])
+
+    users = User.where(organisation: old_organisation)
+    users.update_all(organisation_id: new_organisation.id)
+
+    puts "Moved #{users.count} users from #{old_organisation.slug} to #{new_organisation.slug}"
+  end
 end
diff --git a/test/lib/tasks/data_hygiene_test.rb b/test/lib/tasks/data_hygiene_test.rb
index 9fb3dbc71..2ae674b46 100644
--- a/test/lib/tasks/data_hygiene_test.rb
+++ b/test/lib/tasks/data_hygiene_test.rb
@@ -16,4 +16,20 @@ class DataHygieneTaskTest < ActiveSupport::TestCase
       assert organisation.reload.closed?
     end
   end
+
+  context "#bulk_update_user_organisation" do
+    should "update the organisation for matching users" do
+      old_organisation = create(:organisation, slug: "department-of-health-old")
+      new_organisation = create(:organisation, slug: "department-of-health-new")
+      another_organisation = create(:organisation, slug: "department-of-other-stuff")
+
+      user_1 = create(:user, organisation: old_organisation)
+      user_2 = create(:user, organisation: another_organisation)
+
+      Rake::Task["data_hygiene:bulk_update_user_organisation"].invoke(old_organisation.content_id, new_organisation.content_id)
+
+      assert_equal new_organisation, user_1.reload.organisation
+      assert_equal another_organisation, user_2.reload.organisation
+    end
+  end
 end