A Republican state Senator from Minnesota who said he would vote for equal marriage and was the target of a new pledge by anti-equality group the National Organization for Marriage to defeat him, has said he will not bow to the financial pressure.

Minnesotan state Senator Branden Petersen, announced last week that he intended to vote in favour of marriage equality if it comes to a vote in the state.

The National Organization for Marriage (NOM) said it would pay $500,000 (£329,772) to defeat any GOP legislator voting for equality in potential upcoming votes, and woud support any Democrat voting against equal marriage.

The group specifically targeted Senator Petersen, threatening that it would be a bad move politically to lend his support to marriage equality.

“Republicans like Branden Petersen don’t realise that not only is voting to redefine marriage a terrible policy, it is also a career-ending vote for a Republican,” the NOM said in a statement.

“NOM will do everything in our power to defeat any Republican who votes in favor of same-sex marriage.”

The Senator responded to say: “Regardless of the amount, whether it’s $500,000 (£329,772) or $50 million (£33 million), my vote is not going to bought either way. I’m going to do what’s right,” Petersen said. “If they want to throw away $500,000, then that’s their decision.”

Upon announcing his support for equal marriage, Senator Petersen said: “At this point, I am concerned about doing the right thing. I have a certain amount of peace about that, and I will let the chips fall where they may.”

The NOM cited New York state Republican Senators, three of whom were no longer in office, however some have pointed out that those claims are not entirely true, as one of those Senators retired.

Richard Carlbom, campaign manager for Minnesotans United said: “This desperate attempt by the National Organization for Marriage to financially bully legislators to vote against their values clearly shows they know that Minnesotans want to secure the freedom to marry for same-sex couples in 2013.”

“Leaders who help secure the freedom to marry will be rewarded by voters — just like in every other state.”

On 6 Novemnber, voters in Minnesota voted ‘no’ on Amendment 1, a constitutional amendment that would have defined marriage as being a union solely between a man and a woman.

WashingtonMaine and Maryland legalised equal marriage in referendums in those states on the same day.