The California law known as Proposition 8 is scheduled to be back before the 9th U.S. Circuit Court of Appeals in San Francisco Thursday as justices consider several lingering issues of the case.
The measure, passed by California voters last year, says marriage is between a man and a woman and bans same-sex marriage.
Opponents of gay marriage are trying to overturn a judge's ruling against Proposition 8, which set aside the gay marriage ban. They argue that the judge, a homosexual involved in a same-sex relationship, was biased when he ruled the law unconstitutional.
The appeals court is also expected to address whether Prop 8 supporters have the legal right to press the appeal without support from the Golden State's top officials. The state's supreme court has already ruled in their favor.
Court watchers believe Prop 8 could eventually wind up before the U.S. Supreme Court, which may force it to rule on the issue of same-sex marriage.