San Francisco - Opponents of same-sex marriage have collected enough signatures for a statewide vote to ban gay unions in California's constitution, California Secretary of State Debra Bowen said Tuesday.

The November ballot initiative would overturn a May 15 ruling by the California Supreme Court that banning same-sex marriage violated the constitutional rights of gay people. The ballot initiative would amend the constitution to override that ruling and define marriage as a union between a man and a woman.

California officials are due to start performing gay marriages on June 17, when the court ruling takes effect. Traditional marriage licenses will be amended to refer to Party A and Party B instead of the previous gender-specific bride and groom.

The ballot on the constitutional amendment is sponsored by the California Family Council. But it likely faces an uphill battle after a recent field poll found that 51 per cent of registered voters approve of same-sex marriage, while just 42 per cent disapprove.

In 2000, voters approved an earlier ban on the unions, but that was overturned by the court's decision. (dpa)