The California Supreme Court has ruled that same-sex couples have the right to marry, overturning a state ban on gay marriage. Mike O'Sullivan reports, California will become the second U.S. state, after Massachusetts, to allow gay and lesbian unions.

Gay rights supporters celebrate outside the California Supreme Court, 15 May 2008

Outside the San Francisco courtroom, supporters of same-sex marriage applauded the four to three decision by the state supreme court.

The court overturned a gay marriage ban that was based on a 1977 state law and a voter-approved initiative from 2000. Both limited marriage to unions between a man and a woman.

California has a domestic partner law that gives same-sex couples many of the rights of married couples, but the majority on the court said that is not enough, and that sexual orientation should not be a bar to marriage.

In 2004, San Francisco mayor Gavin Newsom defied the state ban and his city issued marriage licenses to nearly four thousand same-sex couples before the courts stopped the practice. Two dozen gay and lesbian couples, the city of San Francisco, and gay rights organizations filed suit challenge to law.

One group opposed to the ruling called the majority justices out of touch. Another called the decision arrogant judicial activism that it said destroys the civil institution of marriage. Conservative organizations are circulating petitions to put a measure on the November ballot that would outlaw same-sex marriage in the California constitution. If the voter measure passes, it would overrule Thursday's decision.

California governor Arnold Schwarzenegger is opposed to changing the constitution and said Thursday he will respect the court's decision and uphold the ruling.

Kate Kendell is executive director of the National Center on Lesbian Rights, lead counsel for the plaintiffs in the same-sex marriage case. She says gay and lesbian unions could begin in California in as little as 30 days. She notes that a number of U.S. states have amended their constitutions to ban gay marriage, and she says same-sex couples in California will now turn their attention to the election.

"It will require showing up on Election Day in November and beating back this amendment, and I think we will be joined by a legion of friends and allies and coworkers and neighbors and friends and family who will say enough is enough," said Kate Kendell. "We no longer want these kinds of amendments in this nation. We no longer want to be divided. We really do want to come together."

The California decision affects only one state, the nation's most populous. But in this election year, its reverberations will be felt around the country, and it will probably inject the issue of gay marriage into the presidential election.