The justices rejected a request by six members of the firearms rights group Gun Owners of America to throw out a lower court's decision allowing the law to be enforced. U.S. District Judge Glenn Suddaby in October blocked enforcement of much of the law but the Manhattan-based 2nd U.S. Circuit Court of Appeals in December put that decision on hold while the state pursues an appeal.

(Reporting by Nate Raymond in Boston and Andrew Chung in New York; Editing by Will Dunham)