Voting on gay marriage should not be left to MPs' consciences, Nick Clegg has said.
The Deputy Prime Minister and Liberal Democrat leader said his MPs would back legislation legalising same-sex marriages - unlike some of their coalition partners.
Tory MPs will be allowed a free vote to avoid a rebellion from Tory MPs and ministers opposed to the issue.
But Mr Clegg said: "We are not asking any person with religious convictions to sacrifice anything. We are simply saying those who want to show a lifelong commitment to each other should be able to do so."
The Deputy Prime Minister said it was up to Prime Minister David Cameron whether he forced Conservative MPs to support the measure, but vowed Lib Dems would "honour what we have said as a party".
Commons Leader Sir George Young last week confirmed MPs would be offered a free vote, saying: "Along with other issues that involve matters of conscience, it seems to me perfectly proper that this should be subject to a free vote on this side of the House and that is what we plan to do."
But Mr Clegg told BBC1's Andrew Marr Show: "In the same way the civil partnerships legislation which was introduced under Labour was a whipped vote, I personally don't think this is something which should be subject to a great free for all because we are not asking people to make a decision of conscience."
He added: "If this was an issue that somehow the Government was proposing something that would somehow be an imposition on religion or the churches, then of course that would be a matter of conscience. We are not."
Critics have questioned Mr Cameron's commitment to the reform after he conceded to a free vote to quash an expected a rebellion among backbench Tories.
Senior Tory backbencher Mark Pritchard said: "Nick Clegg can try and whip his MPs if he wants to, but David Cameron has given a clear commitment to a free vote for all Conservative MPs. Nothing Nick Clegg says changes that."