Actor Brad Pitt has told a US magazine that people who deny gay and lesbian couples the right to get married do not understand freedom.
In September the screen star donated $100,000 (£65,500) to the campaign against Proposition 8 in California.
The ballot measure, which ended legal gay marriages in the state, passed with 52% of the vote on election day in November.
“People who are against gay marriage do not understand the very freedoms that they themselves are enjoying,” Mr Pitt told W magazine.
“What if someone said, ‘Sorry, no Christianity here? No Judaism. Certainly no Mormons.’
“No one would stand for that, and I wouldn’t allow anyone to say that either.
“I’d fight them in the same way.”
The actor also denied that an affair with Angelina Jolie ended his relationship with Jennifer Aniston.
Mr Pitt claimed he had split from the Friends star before he and Ms Jolie became involved romantically, while they were filming Mr and Mrs Smith.
The California Supreme Court ruled in May that a previous ballot measure passed in 2000 banning same-sex marriage was invalid.
The court said that treating people differently based on their sexual orientation violates the equal protection clause of the California Constitution.
More than 18,000 gay and lesbian couples married in California before November 4th.
Supporters of Prop 8 have asked the court to invalidate those marriages and uphold the democratic results of the November ballot.
Gay rights groups have filed briefs with the California Supreme Court asking it to declare Proposition 8 invald.
The state Attorney General’s position is that certain fundamental rights, including the right to marry, are inalienable, cannot be put up for a popular vote and cannot be applied to invalidate existing marriages.