A federal judge has ordered gay advocacy groups to surrender documents related to Proposition 8, the gay marriage ban narrowly approved by California voters in 2008.

The AP is reporting that Chief US District Judge Vaughn Walker has upheld a magistrate judge's ruling requiring pro-gay marriage groups to hand over Proposition 8 campaign materials to defendants in the high-profile trial considering the ban's constitutionality. Walker made a similar ruling before the January start of the trial, ordering defendants to turn over some documents related to the campaign.

The American Civil Liberties Union and Equality California, the state's largest gay advocate and the lead group behind the campaign against the gay marriage ban, had argued that the documents are confidential internal communications protected by the First Amendment as political speech.

In his 24-page ruling released Monday, Walker disagreed and gave the groups until April 12 to comply.

“To the extent the ACLU and Equality California argue the magistrate's order imposes an undue burden on them, they have failed to substantiate the burden,” Walker wrote.

The ACLU has suggested it would appeal the ruling to the 9th US Circuit Court of Appeals, a move likely to delay closing arguments in the trial, which Walker has yet to schedule.

Plaintiffs argued in January that Proposition 8 violates their constitutional rights. It is the first federal case to consider the constitutionality of a gay marriage ban and is expected to reach the Supreme Court.