add_filter('acf/fields/relationship/query/name=registered_dog', 'event_dog_query_func', 10, 3); function event_dog_query_func ($args, $field, $post_id){ if (isset($_POST) && !empty($_POST) && isset($_POST['owner']) && !empty($_POST['owner'])){ $args['author__in'] = array($_POST['owner']); } return $args; } add_filter('acf/fields/post_object/query/name=registered_dog', 'event_dog_query_func', 10, 3);