Vince Cable: Get on with Lords reform
Cabinet minister Vince Cable has urged Conservative MPs to "get on with" reforming the House of Lords.
Up to 100 backbenchers are expected to rebel against the government when the issue goes to a vote in the Commons on Tuesday, throwing proposals to create elected peers into doubt.
Mr Cable said he thought the coalition would win and that the issue had to be handled in a "businesslike" way.
But Tory MP David Davis said there was no agreement over Lords reform.
The Commons will hold a two-day debate on Monday and Tuesday, with Liberal Democrat leader Nick Clegg championing reform.
The government is proposing almost halving the number of peers, to 450, and to make the House of Lords 80% elected.
However, many Conservatives oppose the plan, suggesting it is flawed and will result in increased conflict between the new body and the Commons.
There is also anger at the government's "programme motion", which would limit the amount of time MPs can spending discussing the issue to 10 days.
This is opposed by Labour, with up to 100 Tories expected to rebel when a vote takes place on Tuesday.
Mr Davis, who is one of the group threatening to do so, told BBC One's Andrew Marr Show that the independence of the Lords to scrutinise legislation was under threat.
He added: "The difficulty is there are so many different ideas about how to do it [reform the Lords]."
The government's proposals would see elected peers in place by 2015.
Mr Davis said that this "gives a lot of power to the parties... which is not what we want".
He added that the issue should be put to a referendum, which could not happen "by 2015".
Fellow Conservative MP Nadine Dorries accused the Lib Dems of "blackmailing" the Conservatives over Lords reform.
She told Sky News the party had said that, if this did not go ahead, it would not allow planned changes to MPs' constituency boundaries, which are said to favour the Conservatives, to go ahead.
But Mr Cable, the business secretary, said: "There's no reason why this vote should be lost. All three parties agree with Lords reform... It's just a question of making sure that the debate proceeds in a businesslike way, and I'm sure it will."
Mr Cable, a Lib Dem, added: "We are not threatening anybody... We are working in a businesslike way with our Conservative partners. We disagree on some things."
He dismissed the Conservative critics of Lords reform, saying: "The main argument they make is that this is a second-order issue... The best reply is to get on with it. Let's just get on with it."
All three main parties promised to reform the Lords in their 2010 general election manifestos.
Labour leader Ed Miliband will argue for a referendum in the debate on Monday.