As expected, anti-gay groups have filed an appeal against a federal court ruling that California’s gay marriage ban is unconstitutional.

Their appeal will be heard by the Ninth Circuit Court of Appeals, which has a reputation for inconsistent decisions.

Chief US District Judge Vaughn Walker ruled on Wednesday that the state’s ban on gay marriage violates equal protection clauses in the US constitution and that moral disapproval is not a valid reason to deny the right to marry.

The Ninth Circuit Court of Appeals consists of 27 judges, a mix of liberals and conservatives, although it is generally seen as a liberal court.

Three judges will be randomly selected by a computer programme to hear the appeal, leaving both sides uncertain as to which way the judgment will go.

Chance could mean the ruling being struck down by three conservative judges and the Supreme Court refusing to get involved.

Judge Walker ruled that his decision should come into effect immediately but agreed to wait until a hearing today to decide whether it should be stayed while opponents appeal.

He has asked both legal teams to submit written arguments ahead of the hearing.

In February, during the 13-day trial, he was outed by the San Francisco Chronicle, which said his sexuality was an “open secret”.

Judge Walker has not commented on the report, but it is being used by anti-gay marriage groups to question his judgment.

The National Organisation for Marriage has insinuated that his sexual orientation may have coloured his ruling, although others contend that the situation is similar to a female judge ruling on abortion or a black judge ruling on racially-motivated offences.

Maggie Gallagher, chairman of the board of NOM, said: “Here we have an openly gay . . . federal judge substituting his views for those of the American people and of our Founding Fathers who I promise you would be shocked by courts that imagine they have the right to put gay marriage in our constitution.

“We call on the Supreme Court and Congress to protect the people’s right to vote for marriage.”

California’s gay marriage ban, known as Proposition 8, passed in November 2008 with 52.3 per cent of California residents voting in favour of it.

During the brief window in which gay marriage was legal, 18,000 gay couples tied the knot. They were permitted to remain married and are not affected by the current case.