Burnley Liberal Democrat MP Gordon Birtwistle has said he will vote against same-sex marriage, becoming the first in his party to do so.
Mr Birtwistle says while he is content with civil partnerships, he disagrees with redefining marriage.
He commented: “I will vote against gay marriage. Civil partnerships are fine. Gay marriage is just not on.”
Earlier this year Liberal Democrat minister Vince Cable said that changing the definition of marriage is unnecessary.
Dr Cable, who is the Secretary of State for Business, said that he thought the “status quo is fine” with civil partnerships.
However he also said if the issue came to a vote, he would back the Government.
In March 2012 the widow of a former deputy leader of the Liberal Democrats resigned from the party after almost 50 years because of its plans to redefine marriage.
In a letter Lady Joan Johnston said gay marriage was the ‘straw that has finally broken the camel’s back’. She had been a Lib Dem member since 1964.
She made the decision following an email from Nick Clegg, in which he claimed one of the party’s achievements will be the first homosexual marriage before 2015.
Mr Clegg has said he wants same-sex marriage to be allowed in both civil and religious premises.
The Government is now set to bring forward a Bill on same-sex marriage in January.