diff -u b/core/modules/field/field.module b/core/modules/field/field.module
--- b/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -405,7 +405,7 @@
         'The %fields field will have data purged during this synchronization.',
         'The following fields will have data purged during this synchronization: %fields.',
         array('%fields' => implode(', ', $field_labels))
-      ));
+      ), 'warning');
     }
   }
 }