diff --git a/docs/api-guide/viewsets.md b/docs/api-guide/viewsets.md
index 22acfe327a..5550c3ceda 100644
--- a/docs/api-guide/viewsets.md
+++ b/docs/api-guide/viewsets.md
@@ -57,6 +57,8 @@ Typically we wouldn't do this, but would instead register the viewset with a rou
     router.register(r'users', UserViewSet, basename='user')
     urlpatterns = router.urls
 
+> **Warning**: Do not use `.as_view()` with `@action` methods. It bypasses router setup and may ignore action settings like `permission_classes`. Use `DefaultRouter` for actions.
+
 Rather than writing your own viewsets, you'll often want to use the existing base classes that provide a default set of behavior.  For example:
 
     class UserViewSet(viewsets.ModelViewSet):