Senior Tory MP Brian Binley has warned in an open letter to David Cameron that the gay marriage agenda risks alienating the Conservative Party's base ahead of the next general election.
The Government outlined its plans to redefine marriage during a debate in the House of Commons on Tuesday.
It was announced that under changes to the law, same-sex marriages would be illegal in the Church of England and Church in Wales, while other religious organisations would be able to "opt in" to offering the ceremonies.
The plans also make it unlawful for religious organisations or their ministers to wed same-sex couples unless their governing bodies have opted in.
The Government also insisted that provisions would be made to ensure that no discrimination claims can be brought against churches that refuse to marry same-sex couples.
Mr Binley, Vice-Chairman of the Business, Innovation and Skills Committee, said the Prime Minister's push for gay marriage had "resulted in the creation of organisational factions within the party squabbling in public over the issue".
He warned that the party's credibility would be at stake if went ahead with redefining marriage in spite of opposition among Tory MPs and supporters.
"Countless activists are feeling driven to give up their much-needed support for the party, and, as any legislation progresses, this injury can only get worse," he said.
"Recent policy developments and the tone of their communication demonstrate a narrative quite absent of anything consistent with the core principles and philosophy of the party.
"We appear to be living from 'headline' to unplanned reaction, and the chaos is harming the party's reputation with our voters.
"It is not just the standing of the leadership which is imperilled through this approach, but our entire political credibility."