Former New York City Mayor Rudy Giuliani and Senators Susan Collins of Maine and Mark Kirk of Illinois are among the more than 300 Republicans who have signed on to an amicus brief urging the Supreme Court to strike down gay marriage bans.

The highest court on Thursday announced that it would hear a case challenging bans in four states – Ohio, Tennessee, Michigan and Kentucky – on April 28, with a ruling expected in June.

Such bans are “inconsistent with amici's understanding of the properly limited role of government,” the brief states.

“Although amici hold a broad spectrum of socially and politically conservative, moderate, and libertarian views, amici share the view that laws that bar same-sex couples from the institution of civil marriage, with all its attendant profoundly important rights and responsibilities, are inconsistent with the United States Constitution’s dual promises of equal protection and due process.”

The brief was organized by former Republican National Committee (RNC) Chairman Ken Mehlman, who said in 2010 that he came out gay to help the conservative case for marriage equality.

(Related: Ken Mehlman insists gay marriage is consistent with GOP values.)

Other notables who signed the brief include Massachusetts Governor Charlie Baker, former Utah Governor Jon Huntsman and GOP donor David Koch. has the full list of signatories.