SAN FRANCISCO -- The California Supreme Court on Tuesday upheld same sex marriages that were already performed but upheld voters' rights to ban gay marriage through the state constitution.

An estimated 18,000 gay couples tied the knot before the law took effect. The ruling suggests that gay couples can be afforded equivalent rights to heterosexual married couples but perhaps under a different name.

Gay rights demonstrators flooded the courthouse before the decision and immediately started protesting the ruling. Holding signs and many waving rainbow flags, they chanted "shame on you." Many people also held hands in a chain around an intersection in an act of protest.

"It's not about whether we get to stay married. Our fight is far from over," said Jeannie Rizzo, 62, who was one of the lead plaintiffs along with her wife, Polly Cooper. "I have about 20 years left on this earth, and I'm going to continue to fight for equality every day."

Rizzo and Cooper had argued that the Legislature should have approved the change to the California constitution because of the vote's impact on the equal protection clause.

But Chief Justice Ron George, writing the 6-1 decision, said the people have a right, through the ballot box, to change their constitution.

"In a sense, petitioners' and the attorney general's complaint is that it is just too easy to amend the California constitution through the initiative process. But it is not a proper function of this court to curtail that process; we are constitutionally bound to uphold it," the ruling said.

The court is the same one that last May ruled it unconstitutional to deny gay couples the right to marry. That led to the constitutional amendment offered on the ballot last November.

"After comparing this initiative measure to the many other constitutional changes that have been reviewed and evaluated in numerous prior decisions of this court, we conclude Proposition 8 constitutes a constitutional amendment rather than a constitutional revision," the ruling said.

Gay rights activists say they plan to return to voters as early as next year with a bid to repeal Proposition 8.

Click here to read the opinion.