Rights groups in California announced Wednesday they would challenge the legality of a newly-passed constitutional amendment that yanks back on the right of gays and lesbians to marry in the state.

Tuesday's passage of Proposition 8 was challenged Wednesday by the American Civil Liberties Union, Lambda Legal and the National Center for Lesbian Rights, who filed a writ petition before the California Supreme Court asking for the amendment to be invalidated.

Gays and lesbians had been marrying at breakneck speeds in California since its Supreme Court had overruled a 2000 voter-approved gay marriage ban. An estimated 18,000 gay couples had tied the knot since the court's May ruling which declared the gay marriage ban unconstitutional.

But gay marriage backers were heartbroken Tuesday when California voters approved the amendment that unties their bonds even as Senator Barack Obama – a gay-affirming candidate – was being elected president.

Voters in Arizona and Florida also approved similar constitutional amendments to ban gay marriage. But in Connecticut, a voter initiative that would force a constitutional convention to discuss altering the constitution to ban gay marriage was unsuccessful. Officials in the state said they would begin satisfying a Connecticut Supreme Court ruling granting gays and lesbians the right to marry on November 12.

Rights groups in California argue the gay marriage ban is invalid because it alters the constitution's “core commitment to equality for everyone by eliminating a fundamental right from just one group, lesbian and gay Californians.”

“If the voters approved an initiative that took the right to free speech away from women, but not from men, everyone would agree that such a measure conflicts with the basic ideals of equality enshrined in our constitution,” Jenny Pizer, a staff attorney with Lambda Legal, said in a statement announcing the challenge.

The rights groups say the gay marriage ban used an improper vehicle – a voter ballot – to alter the constitution. They contend that such a measure is only valid when making superficial changes to the constitution. To change the underlying principles of the constitution, a measure must first be approved by the legislature before being submitted to the voters on a ballot. Proposition 8 radically alters the California constitution by removing rights previously given by the constitution itself, and relied on the voter ballot to accomplish its goal.

“A major purpose of the constitution is to protect minorities from majorities,” said Elizabeth Gill, a staff attorney with the ACLU of Northern California. “Because changing that principle is a fundamental change to the organizing principles of the constitution itself, only the legislature can initiate such revisions to the constitution.”

The rights groups said there is historical precedent for the California Supreme Court to strike down an improper voter initiative. In 1990, a voter-approved initiative that sought to “strip California's courts of their role as independent interpreters of the state's constitution” was overturned by the court.

While California's Attorney General has said the state will honor all legal gay marriage licenses, many believe those marriages are certain to be challenged by gay marriage foes.