Lynch, a Democrat, gave only 80 minutes notice before signing the bill in the state's Executive Council chambers Thursday but nearly 200 supporters showed up to witness the signing, the Nashua (N.H.) Telegraph reported Friday.

"I've listened and heard all the arguments," Lynch said. "I do not believe this bill threatens marriage. I believe this is a matter of conscience and fairness. And my view is that it's never too soon to act to prevent discrimination."

Opponents of the measure said the bill would harm Lynch and the Democratic majority in the legislature come re-election time.

"New Hampshire voters did not have civil unions in mind when they gave Governor Lynch a Democratic majority last fall," Republican State Chairman Fergus Cullen told the Telegraph.

"The Democrats have gone too far, too fast with social policy," he said.

The law, which takes effect Jan. 1, makes New Hampshire, after Vermont, Maine and New Jersey, the fourth state to recognize civil unions for same-sex couples.