Aides to Republican U.S. Sen. Scott Brown say he opposes a federal marriage amendment backed by GOP presidential hopeful Mitt Romney that would define marriage as the union between one man and one woman.
Brown, who opposed gay marriage as a state lawmaker, hasn't said whether he's changed his mind on same-sex marriages, which he called "settled law" in Massachusetts.
Brown said the question whether to legalize gay marriage should be left to individual states.
"Here in Massachusetts, gay marriage has been settled law for nearly a decade, and I continue to believe that states should be able to decide this issue," Brown said in a written statement. "Regardless of how states choose to define marriage, I believe all people should be treated with dignity and respect."
Brown's chief Democratic rival Elizabeth Warren backs gay marriage.
Brown's statement comes as President Barack Obama said he personally supports gay marriage. Aides said the president's shift wouldn't change current policies and he also believes marriage is an issue best decided by states.
Gay rights activists in Massachusetts seized on Obama's statement to criticize Brown.
State Rep. Liz Malia, a Boston Democrat, said Brown's actions don't match his rhetoric.
"As someone who knew Scott Brown as a colleague in the Massachusetts Legislature, I know that Scott Brown has a long, long history of opposing LGBT equality," said Malia, who is gay.
Activists point to Brown's support for the federal Defense of Marriage Act, which prohibits federal recognition of gay marriages.
Massachusetts Attorney General Martha Coakley, a Democrat, has challenged the law saying it denies gay couples married in Massachusetts from obtaining federal marriage benefits.
Brown supporters say he has backed some gay rights initiatives, including joining with Democrats to vote to repeal the military's "don't ask, don't tell" ban on gays serving openly.
But Brown has also opposed gay rights issues.
In 2007, when he was serving in the Massachusetts Senate, Brown voted to place a question on the Massachusetts ballot that would have banned gay marriage. The question never made it onto the ballot.
That vote came years after a 2003 decision by the Massachusetts Supreme Judicial Court that ruled the state's existing ban on same sex marriages violated the Massachusetts constitution.
The ruling allowed gay couples to begin marrying in 2004. Massachusetts was the first state to allow gay marriage.
Brown is a supporter of Romney and credited the former Massachusetts governor with helping him win the 2010 special election to fill the Senate seat left vacant by the death of long-time Democratic Sen. Edward Kennedy.
Romney, who also opposed the legalization of same-sex marriage in Massachusetts, said his views on gay marriage haven't changed.
"My view is that marriage itself is between a man and a woman," the presumptive Republican presidential nominee told reporters Wednesday, adding that he believes states should be able to make decisions about whether to offer certain legal rights to same-sex couples.
"This is a very tender and sensitive topic, as are many social issues, but I have the same view that I've had since - since running for office," Romney said.
During the Republican presidential primary, the National Organization for Marriage asked GOP presidential candidates to sign their marriage pledge including support for a federal marriage amendment defining marriage as the union between one man and one woman.
Romney was among those who committed to the pledge.
This program aired on May 11, 2012. The audio for this program is not available.