A federal appeals court upheld a Maine law that could reveal the donors who financed a $1.8 million movement that helped overturn the state's gay marriage law.
The court rejected arguments from the National Organization for Marriage that being forced to disclose donors who backed the effort was a violation of First Amendment speech rights.
The court's decision on Tuesday means the National Organization for Marriage, which advocates that marriage be defined as being between a man and a woman, could have to reveal the names of people who gave more than $100 to its campaign efforts against same-sex marriage in Maine.
The Maine law says that groups that spend more than $5,000 "for the purpose of initiating or influencing" a referendum must disclose the names of their donors.
The decision by a panel on the U.S. Court of Appeals for the First Circuit in Boston clears the way for the state to conduct an inquiry into whether the group was indeed raising money to influence the ballot initiative.
A lawyer for the conservative group said it would appeal the case to the U.S. Supreme Court.
Maine's legislature legalized same-sex marriage in 2009 but the law was overturned that same year by a "people's veto" in a referendum 53 percent to 47 percent.
As part of that campaign, the Washington D.C.-based National Organization for Marriage steered hundreds of thousands of dollars in contributions to Stand for Marriage Maine.
The group's lawyer, James Bopp Jr., said it was unfair that advocacy organizations should face the same disclosure requirements as political action committees.
"The homosexual lobby has launched a nationwide campaign to harass supporters of traditional marriage," he said. "When they disclose who they are they can reasonably expect to be harassed."
Thomas Knowlton, Maine's assistant attorney general, said the state was pleased that the constitutionality of the law had been upheld.
The same court ruled against the National Organization for Marriage last year in a related case involving disclosure of contributions to individual candidates. The U.S. Supreme Court is expected to decide whether to hear that case by the end of the month.
Same-sex marriage proponents have collected more than 100,000 signatures to put gay marriage back on the Maine ballot again this year.
In neighboring New Hampshire, which legalized gay marriage in 2009, Republicans who control super-majorities in the state legislature are considering a bill that would repeal same-sex marriage.
Six states plus the District of Columbia currently recognize same-sex marriage: New York, Massachusetts, Connecticut, New Hampshire, Vermont and Iowa. Washington's senate was expected to approve a bill legalizing same-sex marriage in that state on Wednesday, and that state's governor also was expected to sign the bill into law.
(Reporting by Jason McLure; Editing By Barbara Goldberg and Paul Thomasch)