Gov. Mitt Romney's (searchtop legal adviser said Tuesday that if local clerks issue marriage licenses to out-of-state gay couples, that will make the marriages void and could result in legal repercussions for the clerks themselves.

Clerks will be required to seek proof of residency (search) or the intention to move to Massachusetts from all couples -- gay and straight -- who are seeking to marry as of May 17, when same-sex weddings (searchbecome legal, attorney Daniel Winslow said Tuesday before the state's first training session for city and town clerks.

The consequences of an illegal marriage could be severe for the couple, particularly if they have children, because of legal questions of support and custody, Winslow said. There also would be legal consequences for the clerks, though Winslow declined to say what those could be.

"What conscientious clerk ever would issue a license in violation of Massachusetts law when the consequences and ramifications to children and innocent parties would be so great?" Winslow said in an interview with The Associated Press. "I simply can't see that any clerk would do that."

The state planned to hold the first of five training session for clerks Tuesday afternoon in Barnstable. At the session, clerks will see the state's new intention-to-marry forms (search), which have been altered to remove gender references and now include a place to show what proof of residence was provided.

The state Department of Public Health plans to advise clerks that written proof is the best documentation, though the sworn oath of the couple applying for marriage is legally acceptable, Winslow said.

Massachusetts law does not allow couples to be married here if their marriage would be illegal in the state where they live.

"This has been a practice that up until now has not been widely followed," Winslow said. "But Massachusetts marriage laws have never been so broad compared to the rest of the nation before."