California's battle over gay marriage returns to court on Thursday, nearly one year after a historic ruling that allowed thousands of same-sex couples to tie the knot.
In the latest chapter of a legal saga that has rumbled on for years, rights lawyers will urge California's Supreme Court to invalidate a referendum that defined marriage as union between a man and a woman.
Oral arguments in the case get underway at 9:00 am (1700 GMT) local time. The court must issue its ruling within 90 days.
The November referendum -- known as Proposition 8 -- came six months after California Supreme Court justices had voted 4-3 in favor of overturning a previous ban on same-sex marriage in the state.
That landmark decision sparked jubilation among gay and lesbian activists, and led to around 18,000 same-sex couples flocking to swap vows as California became only the second US state to allow gay marriage.
However, the issue was forced back on the agenda later by social conservative and religious groups, who successfully gathered enough support for Proposition 8 to be placed on ballots at November 4 polls.
The measure sought to fix the definition of marriage in California to a union between a man and a woman. When the measure was approved -- by a margin of 52.5 to 47.5 percent of the vote -- the status of same-sex marriages was cast into doubt.
A coalition of rights activists, city and state officials are challenging the legality of Proposition 8 on the grounds that the rights of minorities should not be vulnerable to a simply majority vote.
"It is one of the most important cases in the history of the California Supreme Court," American Civil Liberties Union Mark Rosenbaum told the Los Angeles Times on Wednesday.
"The core tenet of our constitutional democracy is that fundamental rights of historically disadvantaged minorities are not dependent on the whim of the majority."
California Attorney General Jerry Brown echoed that position, comparing the dispute to a case in 1964, where courts quashed a voter measure that would have allowed racial discrimination in renting or selling of property.
"As California's Attorney General, I believe the Court should strike down Proposition 8 for remarkably similar reasons -- because it unconstitutionally discriminates against same-sex couples and deprives them of the fundamental right to marry," Brown said.
Opponents of Proposition 8 also argue it is invalid because it was a revision of California's Constitution, not an amendment, and required two-thirds approval by state lawmakers before it was put to a statewide vote.
Leading the team of attorneys pressing for invalidation of Proposition 8 will be Shannon Minter, legal director of the San Francisco-based National Center for Lesbian Rights.
Minter is a transsexual who spent the first 35 years of his life as a female. He married a woman eight years ago and they are raising a daughter. California law allows marriages involving transsexuals.
"This is a huge case," Minter said. "If we were to lose, I'm very fearful about what that would mean for us."
Supporters of Proposition 8 will be led Thursday by Ken Starr, the independent counsel who famously investigated former president Bill Clinton in the Monica Lewinsky scandal.
"The people ultimately decided," Starr said in a court brief. "Under our system of constitutional government, that is the end of the matter."