Prime Minister David Cameron says he intends to press ahead with reforms of the House of Lords, despite a threatened rebellion among some of his Conservative MPs.
An all-party parliamentary committee has recommended replacing the existing upper chamber of some 800 unelected members with a streamlined upper house of 450 - the majority of which would be elected.
The principal recommendation, by the joint select committee, is opposed by a number of Conservative MPs, who fear a largely elected Lords would dilute the importance of the House of Commons.
One Tory, Nadhim Zadawi, is calling instead for the number of peers to be reduced and an independent body created to appoint members.
He said: "The moment you introduce an elected second chamber... that will dilute the primacy of the Commons and could cause gridlock."
Some senior Conservatives are understood to be deeply unhappy and might be prepared to resign their posts rather than support the proposed reforms, which will be incorporated in a bill in the Queen's speech next month.
But the prime minister, facing pressure from his coalition partners to make his party colleagues toe the line, indicated that the government would pursue the reforms.
His spokesman said: "This is part of the coalition agreement and it is our intention to press ahead with reforming the House of Lords."
Deputy Prime Minister Nick Clegg said dissenting Tories should act in the same spirit as his own Liberal Democrat MPs had done in supporting coalition measures they did not necessarily like.
He said: "I have asked Liberal Democrat MPs and peers to back a number of things - the NHS Bill, other things - that they didn't like at all.
"But I did it because it was in the spirit of the coalition, and I would ask all people from all sides of the coalition government to continue to govern in that spirit because it is what I think the British people want."
Mr Clegg and Mr Cameron are against holding a referendum on any reform - another key plank of the committee's recommendations.
But, like Mr Cameron, the deputy prime minister indicated that he would not stand in the way of a vote.
He said it was for "the people who want to advocate a referendum... to explain why we should spend millions of pounds of taxpayers' money on this and why we should create the monumental distraction of a referendum on an issue where all the parties agree and where our central focus remains sorting out the economic mess we inherited".
The joint committee recommended that 80 per cent of the 450 members of the new upper house should be elected, leaving only 20 per cent nominated.
It recommended that they should be paid a salary of between £40,000 and £65,000 rather than an attendance allowance and serve 15-year non-renewable terms.
Eight of the committee's 26 members voted against a referendum before the reforms could be implemented.
There was a small majority in favour of electing some of the members of the upper chamber, and the committee backed the government's proposal for the elections to use the single transferrable vote (STV) system of proportional representation.