The Associated Press:

Washington state is likely to become the seventh state to legalize same-sex within the next two weeks, but opponents have already promised a ballot challenge would halt any summertime weddings.

As supporters celebrated the Senate's 28-21 vote passing the measure on Wednesday night, a coalition of religious groups promised to start collecting referendum signatures as soon as the measure is signed into law. The bill still has to be approved by the House, but with the tougher hurdle of the Senate already cleared, that second vote is just a formality.

Gov. Chris Gregoire announced support for the bill last month, and said she would sign it into law.

The Washington, D.C.-based National Organization for Marriage, noting its involvement in ballot measures that overturned same-sex marriage in California and Maine, issued a statement Thursday promising to work with groups in Washington to qualify a referendum to overturn the likely new law.