David Cameron should drop controversial proposals to introduce same-sex marriage, according to a poll of grassroot Conservative members.
The study, released on the eve of the party's annual conference, found that 71% of Tory constituency chairmen think the policy to redefine marriage should be abandoned, while 47% believe the Prime Minister's stance on the issue had cost members.
The Coalition for Marriage poll also found that just over seven in 10 chairmen believed the plans to make gay marriage legal has damaged Mr Cameron's standing with the party, with just 11% saying it had enhanced it.
Colin Hart, campaign director of the campaign group said: "What this latest poll reflects is the growing unease amongst grassroot Conservatives about the way the PM is trying to force through this policy without any electoral mandate and without any acknowledgement of the profound consequences this change will have."
Six in 10 of constituency chairmen polled by ComRes said they believed legalising same-sex marriage would cost the party votes. Just 4% said the move would boost the party's electoral chances.
Mr Hart continued: "We already know from polling that a majority of the public oppose redefining marriage and Mr Cameron's decision to try and force through these changes is costing him votes.
"One poll put the figure as high as 1.1 million votes, or 30 seats."
More than 600,000 people have signed a petition launched by the Coalition for Marriage petition opposing the move.
Mr Hart added: "If the PM continues to press ahead with this deeply unpopular, radical and profoundly undemocratic proposal, then he can expect to pay the price for this at the ballot box.
"The Prime Minister, who has made a virtue of ditching unpopular or disastrous policies, cannot ignore the mounting opposition to redefining marriage. This includes in his own constituency, his own party and increasingly in our country."
Speaking at a fringe meeting at the Tory party conference in Birmingham on Sunday, former shadow home secretary David Davis said gay marriage was a "distraction".
"Gay marriage is an issue for the Church not for the the state," he said.
ComRes surveyed a random sample of 100 Conservative Party chairmen between September 14 and October 2 2012.
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Chancellor George Osborne and Foreign Secretary William Hague confirmed they would be backing the introduction of same-sex marriage when a free vote is held in the House of Commons.
Mr Osborne told Sky News's Murnaghan programme: "I support gay marriage, I support gay marriage because I believe Conservatives support the institutions of commitment."
Asked if he will vote in favour of gay marriage, Mr Hague told Sky News: "I will support the Prime Minister's position, so yes."
The Foreign Secretary added: "Bear in mind that it is an issue for MPs to decide for themselves - this is not in the Conservative Party a three-line whip.
"This is for every MP to decide for themselves and I think that is the right position on a conscience issue."