A US state's law allowing gay marriage was blocked from taking effect 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 of Washington was to begin allowing same-sex marriages.
Joseph Backholm, chairman of Preserve Marriage Washington, said: "The current definition of marriage works and has worked."
The law, passed by the state legislature and signed by governor Chris Gregoire earlier this year, would make Washington the seventh US state to have legal same-sex marriages.
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 legalised gay marriage this year but is also poised for a public vote in the coming months.