The U.S. Supreme Court has been asked to examine whether class certification is automatically barred when the proposed class definition is “fail safe”—or when membership hinges on a case’s outcome on the merits.

In a class action against Hilton Hotels Retirement Plan, the U.S. Court of Appeals for the D.C. Circuit in April said there is no implied, free-standing rule against such classes inherent in Rule 23 of the Federal Rules of Civil Procedure. Instead, the court said judges should analyze the rule’s requirements to determine if a proposed class is fail safe, and try to revise it to fix any problems.