The constitutional ban on same-sex marriage in California was challenged yesterday, as advocates filed their opening briefs with the state’s highest court.

Briefs have been filed by the city and county of San Francisco, 15 same-sex couples, Equality California and Our Family Coalition.

Anyone who supports the same-sex marriage ban must answer by June 1st.

Once all the briefs are filed, the California Supreme Court will schedule oral arguments on whether the ban on same-sex marriage discriminates against gay men and women.

The brief filed by San Francisco claims that by denying marriage to gay couples, “the state segregates them and their families from the rest of society, continuing to marginalise them.”

The brief also said that the ban “reinforces in the public mind the already entrenched inferior status of lesbians and gay men.”

San Francisco caused a stir in 2004 by issuing marriage licenses to same-sex couples, which were later voided by the state.

In 2005 Superior Court Judge Richard Kramer ruled that the ban serves no rational purpose, and that it is unconstitutional because it denies same-sex couples equality.

This ruling was later overturned by the Court of Appeal, who concluded that the ban does not violate constitutional rights, and only legislators can define the institution of marriage.

The Court of Appeal considered whether the constitution offered a fundamental right to “same-sex marriage.”

The San Francisco brief said that this goes against established precedent.

It said: “Past courts have not treated marriage claims by interracial couples as involving the right to ‘mixed race marriage.'”

The brief issued by the couples urged the court that “marriage should [not] remain exclusively heterosexual merely because it always has been so.”

The Attorney General’s office is duty-bound to defend state law, and so will be arguing against same-sex marriage.

Former assemblyman Larry Bowler, a proponent of the ban, said: “We fully expect the California Supreme Court to destroy marriage for a man and a women.

“At least four justices on that San Francisco bench are against the broad majority of California voters, who want marriage preserved and protected.

“The high court could deal a low blow to the voters by creating so-called same-sex marriages in late 2007 or early 2008.”

Meanwhile, the battle continues in the legislature.

In 2005 the assembly and the senate approved a bill to permit same-sex marriage, which was promptly vetoed by Governor Arnold Schwarzenegger.

PinkNews.co.uk reported last year that Schwarzenegger believed gay couples were entitled to full protection under the law and should not be discriminated against, but that he felt the bill would have reversed a 2000 ballot measure that declared only a marriage between a man and a woman is legal in California.

The bill has been reintroduced and is scheduled for an April 10 hearing before the Assembly Judiciary Committee, but Schwarzenegger has said he will veto it once more.

Massachusetts is the only state in America to have legalised gay marriage. Connecticut, Vermont, New Jersey, California, Maine, Hawaii and the district of Columbia offer legal recognition of same-sex couples such as civil unions.