The justices issued a unanimous order Wednesday granting a request by the Ninth U.S. Circuit Court of Appeals in San Francisco to decide whether the backers of Proposition 8, the 2008 initiative banning gay and lesbian marriages, have the right under state law to appeal a judge's decision declaring the measure unconstitutional.

The court asked for written arguments between March 14 and May 9 and said it would hold a hearing as early as September, followed by a decision within 90 days.