More than 300 Republicans have signed onto a friend of the court brief at the Supreme Court in support of gay marriage.

The high court has scheduled April 28 for oral arguments in a case challenging the ban on same-sex marriage in Michigan, Ohio, Kentucky and Tennessee. The decision by the justices could potentially be historic and could add to the rulings and other actions that now make it legal for gay couples to marry in 37 states and the District of Columbia.

The effort to show GOP support on the issue is being organized by Ken Mehlman, pictured, a former Republican National Committee chairman who managed George W. Bush’s 2004 re-election campaign, according to TIME Magazine. Mehlman played a similar role in 2013 before the Supreme Court’s decision to California’s Proposition 8, which banned gay marriage.

The Republican signatories include billionaire David Koch, former New York mayor Rudy Giuliani, former Utah governor Jon Huntsman, retired Gen. Stanley McChrystal, top aides in Mitt Romney’s 2012 campaign, and a host of current and former members of Congress.

“One of the points that I hope people appreciate when they read the brief is that supporting marriage equality is, in fact, the conservative position,” Mehlman told The Boston Globe in an interview.