California's Supreme Court has ordered
San Francisco officials to immediately suspend same-sex marriages.
San Francisco has a long-established and highly vocal gay community
The move was made pending a legal review on the issue later this year and comes amid conservative outrage and calls for a constitutional ban.
More than 3,000 ceremonies for gay and lesbian couples have been performed in San Francisco since the city began issuing marriage licences last month.
The court has yet to rule on the legality of these existing marriages.
In its order, the court referred to California's family code which defines marriage as a union between a man and a woman.
San Francisco officials were told "to refrain from issuing marriage licences or certificates not authorised by such provisions".
The justices are not expected to reach a decision on the existing marriages for a couple of months, BBC California correspondent David Willis notes.
They indicated they would also decide whether San Francisco's mayor had had the authority to allow the weddings.
The decision comes after California Attorney General Bill Lockyer asked the state's top court to take up the case.
Mr Lockyer had been acting at the request of Governor Arnold Schwarzenegger, who condemned San Francisco for taking the law into its own hands.
"I believe strongly in the law that we have right now in California, which respects domestic partnership and I think that's a very good law," he said at the time.
San Francisco's mayor said the law was discriminatory
San Francisco's Mayor, Gavin Newsom, gave the go-ahead to issue marriage licences to same-sex couples in February saying current legislation was discriminatory.
His spokesman said at the time Mayor Newsom was only following "the state constitution, which explicitly outlaws discrimination of any kind".
Since 12 February some 3,700 gay couples have been married in San Francisco.
Our correspondent says the Supreme Court's decision is a victory for groups opposed to same-sex marriages.
Such groups tabled several court motions over the last month, seeking to put an end to the ceremonies.