A new study of election results by pro-marriage equality group Freedom to Marry and think tank Third Way suggests that there is no truth in claims that legislators who support same-sex marriage laws will suffer a loss of support from their electorates.

The study looked at New York and Washington, the two states which have passed laws allowing same-sex couples to marry, and have also subsequently had a re-election of their legislators in 2012.

It found that 97% of the legislators who voted to pass same-sex marriage laws succeeded when they ran for re-election, compared to a 90% national average.

85% of the 13 Republicans among the legislators that voted for equality succeeded in being re-elected.

Freedom to Marry president Evan Wolfson said: “Polls have shown that a growing majority of Americans support ending the exclusion of same-sex couples from marriage – and now we know that Americans vote that way at the polls, too. Lawmakers who cast votes for the freedom to marry get voted back in – and on both side of the aisle.

“Elected officials can vote for the freedom to marry and be on the right side of history, secure that supporting the freedom to marry is not only the right vote to cast; it’s also the politically smart vote to take.”

The National Organisation for Marriage (NOM), an anti-equality pressure group, have repeatedly warned that legislators will lose votes by supporting same-sex marriage laws.

They recently said they would pledge $500,000 to defeating any Republicans who said they would vote to legalise same-sex marriage.

NOM particularly targeted pro-equality Republican Senator Branden Peterson, who said his vote would not be bought.

“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.

The claim that supporting marriage equality will lose votes is widely used in the UK as well as the US.

The chair of Conservative Grassroots blamed Tory support for equal marriage on their loss in the Eastleigh by-election, but party leaders denied it had been an issue.

Last week UKIP leader Nigel Farage claimed the Conservatives would only gain back voters if they dropped their support for equal marriage.

MP Nadine Dorries recently called equal marriage “political suicide”.

In February Freedom to Marry said that it hoped to raise $2 million (£1.27 million) to spread across several states debating equal marriage laws.