BOSTON (AP) – Attorney General Thomas Reilly said Friday that his office has sent letters to four rebellious clerks and instructed them to stop issuing marriage licenses to out-of-state gay couples, agreeing to a request from Gov. Mitt Romney.

Officials in Provincetown, Somerville, Springfield, and Worcester have openly defied Romney’s edict forbidding clerks from marrying out-of-state couples.

Reilly said he shares Romney’s interpretation of the 1913 law barring couples from marrying in Massachusetts if their union would not be recognized in their home state, and he plans to enforce it.

“Let me make it very clear here, if there are violations of the law, the law will be enforced,” Reilly said Friday, a day after Romney sent him 10 marriage applications filed by out-of-state couples.

Reilly declined to say what enforcement action he would take, but legal experts said he could seek a court injunction ordering clerks to stop. If they continued to issue the licenses, he could charge them with contempt, or in the extreme, with a criminal violation. But the attorney general said he couldn’t imagine putting any clerk in jail.

“We expect the clerks to respect the law,” he said.

Springfield clerk William Metzger said Thursday that he would stop issuing licenses if Reilly, the state’s chief law enforcement officer, agreed with Romney’s interpretation of the 1913 law.

Officials in Provincetown, Somerville and Worcester did not immediately return calls Friday seeking comment on whether Reilly’s request for compliance would sway them to stop issuing licenses.

In each of the four communities, the clerks have issued licenses to out-of-state couples as long as they sign the “Intent to Marry” form, saying that they know of no impediment to their marriage.

Gay marriage became legal in Massachusetts Monday by edict of a state high court decision issued last November, declaring it unconstitutional to bar same-sex couples from matrimony.

Like the Republican governor, Reilly – a Democrat – said that all marriage licenses issued to out-of-state couples will be considered invalid.

Reilly had previously said at least the 38 states that have passed Defense of Marriage Acts would be forbidden from marrying in Massachusetts.

On Friday, he said that no out-of-state couples can marry here under state law and the policy of the Department of Public Health, which dictates marriage law.