It's been hard going for proponents of a California constitutional amendment that bans gay marriage in Chief U.S. District Judge Vaughn Walker's courtroom in San Francisco. On Wednesday Walker handed them their latest setback when he refused to dismiss a challenge to Proposition 8, the voter-approved measure that bans gay marriage, gay weekly Bay Area Reporter reported.

Attorneys representing urged Walker to dismiss the challenge because Proposition 8 does not violate the U.S. Constitution. They argued that the state's restriction of marriage to heterosexual couples fosters procreation. Proposition 8, they said, does not discriminate against gay and lesbian couples.

Plaintiffs say Proposition 8 “was only made on the grounds of animus toward same-sex couples,” Defense Attorney Charles Cooper said. “This claim we resist and reject.”

Walker disagreed, saying that key issues such as how restricting marriage to heterosexual couples fosters procreation could only be answered at trial. And he lanced Cooper's main argument, telling him that “procreation doesn't require marriage.”

The lawsuit was filed in May by a lesbian couple and a gay couple who would like to marry in California but were denied a license because of the ban. The couples are represented by Ted Olson and David Boies. Olson has repeatedly said he believes the case will ultimately be decided by the Supreme Court.

Last month, Walker ordered the group to produce internal emails, memos and records associated with its strategy to ban gay marriage in the state. Cooper, a lawyer with the Christian conservative group the Alliance Defense Fund, argued that making Proposition 8 discussions between top campaign officials public would violate the group's free speech rights and subject supporters to harassment. has appealed Walker's ruling.

In August, Walker scheduled a January 11, 2010 trial date, but the group's appeal might delay the trial's start.