David Cameron's gay marriage proposals are expected to divide the Conservative Party at Tuesday evening's Commons vote.
But while most of the attention is focused on the "rebellion" on the Tory benches, plenty of Labour MPs - and a couple of Lib Dems - are also opposed.
According to the Labour List website, 14 Labour MPs are set to vote against gay marriage, putting them at odds with the party leadership.
The list includes shadow ministers Tony Cunningham, Stephen Pound and Rob Flello, and more Labour MPs are expected to abstain.
The three main parties are each allowing their MPs a free vote, meaning there is no official rebellion against the party leaderships.
Nonetheless, there is discord even in the Liberal Democrat ranks. Burnley MP Gordon Birtwistle has made no secret of his opposition to the plans, telling his local newspaper: “I will vote against gay marriage. Civil partnerships are fine. Gay marriage is just not on.”
Southport MP John Pugh is also against the proposals, on the grounds that the law change "weakens the link between marriage and the family."
The Coalition for Equal Marriage, which has been tracking MPs' voting intentions, says a further nine Lib Dem MPs have yet to declare their intentions.
More anti-gay marriage votes will come from MPs from Northern Ireland, notably the Democratic Unionist Party, despite the fact that the rules will not automatically apply there.