Olympia - Washington state's law allowing gay marriage was blocked from taking effect on Wednesday as opponents filed more than 200 000 signatures seeking a public vote on the issue in November.
Preserve Marriage Washington turned in the signatures just a day before the state was to begin allowing same-sex marriages.
"The current definition of marriage works and has worked," said Joseph Backholm, the chair of Preserve Marriage Washington.
The law, passed by the Legislature and signed by Governor Chris Gregoire earlier this year, would make Washington the seventh US state to have legal same-sex marriages.
Groups plan to fight law
State officials will review the signatures to determine whether they are enough to qualify for a public vote, though the numbers suggest the measure will make the ballot easily.
National groups have already promised to fight the law, including the National Organisation for Marriage, which was involved in ballot measures that overturned same-sex marriage in California and Maine.
Washington state has had domestic partnership laws since 2007, and in 2009, passed an "everything but marriage" expansion of that law, which was ultimately upheld by voters after a referendum challenge.
Gay marriage is legal in New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont and Washington, DC. Maryland legalized gay marriage this year but is also poised for a public vote in the coming months.
In New York City, meanwhile, a federal judge joined a growing chorus of judges across the US on Wednesday by striking down a key component of a federal law denying benefits to partners in a gay marriage.
Failure of law
US District Judge Barbara Jones said the federal Defence of Marriage Act's efforts to define marriage "intrude upon the states' business of regulating domestic relations".
She added that "that incursion skirts important principles of federalism and therefore cannot be legitimate, in this court's view".
The judge said the law fails because it tries to re-examine states' decisions concerning same-sex marriage. She said such a sweeping review interferes with a system of government that places matters at the core of the domestic relations law exclusively within the province of the states.
The ruling came in a case brought by Edith Windsor, a woman whose partner died in 2009, two years after they married each other in Canada. Windsor brought the lawsuit after her late spouse, Thea Spyer, passed her estate to Windsor.
Because of the federal law, Windsor did not qualify for the unlimited marital deduction and was required to pay $363 053 in federal estate tax on Spyer's estate. Windsor sued the government in November 2010.
As part of her ruling, Jones ordered the government to pay Windsor the money she had paid in estate tax.
The government declined to comment through Ellen Davis, a spokesperson for government attorneys in Manhattan.
An avalanche of decisions
Civil rights groups praised the ruling. The American Civil Liberties Union included comments from Windsor in its release.
James Esseks, director of the ACLU Lesbian Gay Bisexual Transgender Project, said the ruling "adds to what has become an avalanche of decisions that Doma can't survive even the lowest level of scrutiny by the courts".
The ruling came just days after a federal appeals court in Boston found the law's denial of federal benefits to same-sex couples unconstitutional. The decision by the 1st US Circuit Court of Appeals affirmed a federal judge's 2010 ruling.
The law was passed after a 1993 decision by the Hawaii Supreme Court made it appear Hawaii might legalise gay marriage.
Since then, many states have instituted their own bans on gay marriage, while eight states have approved it, led by Massachusetts in 2004 and continuing with Connecticut, New York, Iowa, New Hampshire, Vermont, Maryland, Washington state and the District of Columbia.
Maryland and Washington's laws are not yet in effect and may be subject to referendums.