The decision marks a victory for advocates of gay marriage, who charge that the November 2008 voter-approved ban violates the constitutional rights of same-sex couples.
The judge's decision will return the battle over Prop. 8 to the courtroom much sooner than many had expected – and long before gay-rights groups have a chance to overturn Prop. 8 at the ballot box.
The gay-rights community clearly support the spirit of the case brought by attorneys David Boies and Theodore Olson, better known for representing opposing sides in the Bush v. Gore 2000 election challenge. But the two lawyers have prevented the three key gay-rights groups from becoming actively involved, concerned that they would slow down the process.
Lambda Legal, the American Civil Liberties Union, and the National Center for Lesbian Rights filed a joint petition with the court to become plaintiffs in the case. But Messrs. Boies and Olson, representing two gay California couples denied a marriage certificate, opposed the petition.
US District Judge Vaughn Walker backed this decision, though he did allow the city of San Francisco to become a plaintiff. On the other side of the case, he denied a petition from supporters of Prop. 8 to join the defense.
Molly McKay, spokeswoman for the gay rights group Marriage Equality USA, says it's significant that San Francisco is joining the plaintiffs because it could provide evidence that documents how the gay marriage ban affects municipalities.
Reports suggest that the city's attorney would attempt to document the public health costs from psychological distress caused by anti-gay marriage amendments.
"This has real life consequence for real people," says Ms. McKay. What's more, she says, the case "will provide us an opportunity to keep this issue at the forefront of people's minds" as work continues to repeal Prop. 8 at the ballot box.
This lawsuit was filed a few days before Prop. 8 was upheld by the California Supreme Court in May. But the legal argument made previously was that Prop. 8 – approved by 52 percent of voters – amounted to an unconstitutional revision of the state's charter.
The argument made by Boies and Olson are that Prop. 8 denies their clients "the basic liberties and equal protection under the law that are guaranteed by the Fourteenth Amendment of the Unites States Constitution."
Both Gov. Arnold Schwarzenegger and California Attorney General Jerry Brown are named as defendants. Mr. Brown has said he won't defend against the suit, and Governor Schwarzenegger said that he wants to remain neutral.
But on Wednesday Judge Walker said that "the governor's thoughts and views would be very much welcome and appreciated."