The White House on Thursday filed a friend-of-the-court brief with the Supreme Court, marking the first time a U.S. president has urged the high court to expand the right of gays and lesbians to wed.
California is one of eight states that give gay couples all the benefits of marriage through civil unions or domestic partnership but don't allow them to wed. The denial of marriage to same-sex couples, "particularly where California at the same time grants same-sex partners all the substantive rights of marriage, violates equal protection," the administration said.
Apple, Google, Facebook, Amazon and hundreds of other businesses are also filing briefs in support of gay marriage, as are well-known Republicans such as Jon Huntsman, Meg Whitman and Clint Eastwood.
Proposition 8 goes before the Supreme Court in late March. If the court overturns the voter-approved Prop. 8, it would likely result in gay marriage becoming legal in the seven other states: Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon and Rhode Island.
The Associated Press contributed to this report.