The Supreme Court has temporarily blocked recording of the Proposition 8 trial in California, which begins today.

The trial will examine whether a ban on gay marriage in the state is unconstutitonal, but opponents have argued that broadcasting proceedings may leave them open to intimidation and harassment.

Judge Vaughn Walker, presiding over the case, ruled last week it should be broadcast on YouTube with a delay of up to one day, saying the case was important enough that people should be able to watch it.

He added that those who did not want to be shown would have their faces blacked out.

But today, the Supreme Court banned the broadcasting for at least the first few days, saying judges needed more time to consider the issue.

The ban will remain in place until at least Wednesday.

The case has been brought by two gay couples, Kris Perry and Sandy Stier, of northern California, and Paul Katami and Jeff Zarrillo, who live in southern California.

Their lawyers, Ted Olson and David Boies, are expected to argue that banning gay marriage is not a legitimate government interest and that civil unions are not an adequate substitute.

Gay marriage was legalised in California in May 2008. Voters banned it under Proposition 8 the following November.

As the trial began this morning, Equality California executive director Geoff Kors issued a statement calling for the “grossly unjust” law to be struck down.

He said: “Today we are reminded of the devastation Prop 8 has inflicted upon same-sex couples and their families. Anti-gay extremists targeted a minority group, stripped away a precious freedom and relegated lesbian, gay, bisexual and transgender Americans to second-class status with a divisive agenda built on fear mongering and a blatant disregard for the truth.”

“The time has come for elected leaders to empower all Americans, regardless of sexual orientation or gender identity.

“Once again, we call on the Obama administration to join Equality California and others in urging the federal courts to strike down this grossly unjust law.”

If the case is successful in the San Francisco district court, it is deemed unlikely to succeed in the Supreme Court, where conservative judges have been keen to support all pro-gay initiatives other than marriage.

More than 30 US states explicitly ban gay marriage. If the case is successful, it would reverse years of such legislation. Only five US states currently allow gay couples to marry.