Gay rights advocates are urging the court to overturn the ban, approved in November as Proposition 8, on the grounds it was put before voters improperly, or at least prematurely. Under state law, the legislature must approve significant constitutional changes before they can go on the ballot.

Proposition 8's sponsors, represented by former Pepperdine law school dean and Whitewater independent counsel Kenneth W. Starr, said it would be a miscarriage of justice for the court to overturn the results of a fair election.

The ballot initiative, which passed with 52 percent of the vote, changed California's constitution to trump last year's 4-3 Supreme Court decision that legalized gay marriage. The court found that denying same-sex couples the right to wed was an unconstitutional civil rights violation.