A federal judge in San Francisco has refused to dismiss a lawsuit challenging Proposition 8, the voter-approved ban on same-sex marriage in California.

Backers of the measure had sought to have the suit thrown out.

They contend same-sex marriages are a threat to traditional marriages. The plaintiffs argue the amendment discriminates against gays.

U.S. District Judge Vaughn R. Walker has ordered a trial on whether the measure denies fundamental rights to gays and lesbians. That trial is set for January.

Walker previously ordered the Proposition 8 campaign to disclose its internal memorandums and communications to gay rights lawyers.

The campaign is appealing that order to the U.S. 9th Circuit Court of Appeals on First Amendment grounds.