The first word on whether California's same-sex marriage ban passes scrutiny under the U.S. Constitution is scheduled to come down Wednesday when a federal judge issues his ruling in a landmark case.

Chief U.S. District Judge Vaughn Walker has reached a decision on whether to uphold or overturn the voter-approved ban known as Proposition 8 and plans to publish his opinion in the afternoon, court spokeswoman Lynn Fuller said.

His verdict comes in response to a lawsuit brought by two same-sex couples and the city of San Francisco seeking to invalidate the law as an unlawful infringement on the civil rights of gay men and lesbians.

Proposition 8, which outlawed gay marriages in California five months after the state Supreme Court legalized them, passed with 52 percent of the vote in November 2008 following the most expensive campaign on a social issue in U.S. history.

Attorneys on both sides have said an appeal was certain if Walker did not rule in their favor. The case would go first to the 9th U.S. Circuit Court of Appeals then the Supreme Court if the high court justices agree to review it.

Anticipating such a scenario, lawyers for the coalition of religious and conservative groups that sponsored Proposition 8 in 2008 filed a legal brief Tuesday asking Walker to stay his decision if he overturns the ban so same-sex couples could not marry while an appeal was pending.