The Supreme Court split along ideological lines Wednesday as it barred a federal judge in San Francisco from broadcasting a high-profile trial involving same-sex marriage.

The court issued an unsigned opinion that said lower courts had not followed proper procedure in approving plans for the broadcast. The trial is to consider the constitutionality of Proposition 8, California's ban on same-sex marriage, and the Supreme Court cited arguments from proponents of the ban that releasing video of witnesses could subject them to harassment and even physical danger.

The court's liberal bloc -- joined for the first time in an ideological split by Sonia Sotomayor, the new justice -- issued a strong dissent. It said the court's "extraordinary legal relief" was unjustified.

The majority "identifies no real harm" from televising the trial, "let alone irreparable harm to justify its issuance of this stay," wrote Justice Stephen G. Breyer, who was joined by Sotomayor and Justices John Paul Stevens and Ruth Bader Ginsburg. "And the public interest weighs in favor of providing access to the courts."

The court on Monday blocked U.S. District Judge Vaughn R. Walker's plan to stream live video from the trial, which started that day, to five courthouses across the country and to later release the proceedings for broadcast on YouTube. The justices' more complete ruling came at the end of the day Wednesday.