BOSTON -- When Massachusetts became the first state to issue marriage licenses to gay couples in 2004, it left one big roadblock in place: Out-of-state couple needed not apply.

Now an effort is gaining momentum to repeal a 1913 state law that has banned most out of state gay couples from getting married. The law says couples cannot be married in Massachusetts if their unions would be illegal in their home states.

The Democratic leaders of the House and Senate and Gov. Deval Patrick support a repeal, which could come up for a vote as early as Tuesday in the state's Senate.

Opponents of gay marriage fear eliminating the law would open the gay marriage floodgates.

Marc Solomon, executive director of MassEquality, said he's confident the repeal bill will reach Patrick's desk before the end of the formal session July 31.

Kris Mineau, president of the Massachusetts Family Institute, which opposes same sex marriage, said the law is in sync with federal constitutional protections guaranteeing individual states the right to define marriage.