BOSTON (AP) – Prosecutors from Attorney General Tom Reilly’s office have launched a criminal investigation to determine whether workers gathering support for an anti-same-sex marriage amendment forged the signatures of some voters last year.

The investigation stems from allegations by some voters that their names were on signature lists despite the fact that they said they never signed the petition. It would not affect the outcome, since supporters had more than twice as many certified signatures as they needed to send the question for legislative approval for the 2008 ballot.

The question would amend the state constitution to ban same-sex marriage, overturning the state’s historic court ruling. Massachusetts is the only state to allow same-sex marriage.

“Because some of these concerns raised allege the crime of forgery, these allegations were referred to our Criminal Bureau,” Assistant Attorney General Stephanie Lovell said in a letter to Secretary of State William Galvin.

Lovell said investigators from the bureau have “contacted the complaining party to further understand the basis for the allegations.” A meeting with activists from MassEquality, a group which supports same-sex marriage, was planned shortly thereafter.

A call to Kris Mineau, president of the Massachusetts Family Institute, the main backer of the amendment, was not immediately returned.

Marc Solomon of MassEquality said the group has heard from more than 2,000 people who said they either didn’t sign the petition or were tricked into signing it.

“People were duped by trained professional signature gatherers,” he said.

Lovell was responding to a letter sent to Reilly from Galvin. Galvin said he wanted to report the allegations after receiving complaints from voters.

He said the complaints broke down into two categories. One group were voters who said they were tricked into signing the anti-same-sex marriage petition after being told it was an amendment to allow grocery stores to sell wine. The second group of voters said their signatures were simply forged.

Galvin said that while the number of voters making the allegations wouldn’t affect the outcome of the same-sex marriage question, the allegations of forgery are a possible violation of state laws.

At a Statehouse hearing last October, supporters and opponents of the anti-same-sex marriage initiative traded accusations of dirty tricks. Opponents said signature gathers used “bait and switch” tactics to dupe voters into signing the question, while supporters said gay activists stole blank petitions, defaced others to invalidate signatures, and shoved and spit on signature gatherers.

In November, the state Senate approved a bill designed to outlaw “bait and switch” tactics by paid signature gathers. The bill was sent to the House.

Supporters of the anti-same-sex marriage initiative collected more than 170,000 signatures. Of those, 147,000 were certified. They needed only 65,825 certified signatures.

Before it gets on the ballot, the question must win the backing of at least 50 members of the legislature in two successive sessions.