David Cameron should work to win back people who support marriage between one man and one woman, the Grassroots Conservatives group has said.
Bob Woollard, who leads the organisation, said new laws were needed to “protect those who believe in traditional marriage”.
In a letter to the Prime Minister, Woollard warned that people have left the Conservatives over same-sex marriage and were voting for UKIP, or not at all.
“I am personally convinced that the Conservative Party has little chance of winning a majority at the General Election unless you reach a sensible accommodation on this subject”, Woollard wrote.
Before the legislation to redefine marriage was passed, Woollard cautioned that some people would never vote Tory again over the issue.
Woollard, who is a former chairman of the Wycombe Conservative Association, urged David Cameron to “win back those you have alienated” over matters such as same-sex marriage.
The letter was sent in October, but according to Woollard no reply has yet been received.
His remarks echo those of Sir Edward Leigh MP who, earlier this year, suggested that the Conservative Party should take more care “not to infuriate” supporters, and called for it to promote traditional marriage.
Last month Charles Moore, a former editor of The Daily Telegraph, commented that the main political parties treat opponents of same-sex marriage as “moral inferiors”.
Moore said that the “balance” of civil partnerships was “violated by the way that Mr Cameron casually imposed gay marriage”.
“His approach insulted settled beliefs, and therefore wounded him politically more than people like to state directly”, he added.
In May this year a poll found that almost three in ten voters said Mr Cameron’s same-sex marriage policy made them less likely to vote Conservative.
Colin Hart, Campaign Director of the Coalition for Marriage, commented at the time: “This poll is further proof that David Cameron’s undemocratic policy is still causing considerable electoral pain to the Conservative Party and is driving voters to Nigel Farage and UKIP.”