As historic plans for change were unveiled yesterday, Downing Street also explicitly warned for the first time that the Coalition would sack any rebels with Government jobs, such as ministerial aides.
A Number 10 source denied there had been "nods and winks" to Tory MPs that they could fail to back the Government on the issue.
When it came to future prospects, voting against the Bill would be an "interesting career choice", the source added.
There were also strong indications that MPs would be expected to support all parts of the Bill as it makes what is expected to be a difficult journey through the Commons.
Conservatives are furious at what they see as priority being given to what they consider a LibDem obsession at a time of major economic difficulties.
Tory MP Eleanor Laing denounced the plans, warning that having two elected chambers would "reduce democracy, and reduce the accountability of Parliament to the people".
Others explicitly refused to back the Bill.
Conor Burns, parliamentary private secretary to Northern Ireland Secretary Owen Paterson, said he would not be deterred from rebelling by the threat of the sack.
"If I lose my job for something that was a mainstream view within the Conservative Party in the last parliament, which serving Cabinet ministers held as their view, so be it," he said.
Justice Secretary Ken Clarke appealed to rebels not to make what he said would be a "terrible mistake" to "lark about and upset the Liberals".
Mr Clarke also appeared to suggest the new proposals were not set in stone, warning that the process would involve compromise over a number of major issues, such as the role of bishops.
Last night there was also confusion about what members of the reformed chamber would be called.
Officials indicated that the upper house itself would continue to be known as the House of Lords.
However, they suggested that members would not be able to call themselves "Lord", although some could if they have been dubbed so though the Honours system.
A Cabinet Office spokesman said it would be up to Parliament to decide whether they would be referred to as Members of the House of Lords (MHLs) or another title, such a senator.
Earlier, David Cameron had warned supporters they had to "get out there and back" the changes, which the Tories included in their last election manifesto, or face defeat.
He also criticised Labour for attempting to delay the Government's plans.
Labour has confirmed that it will back the proposals but oppose moves to deal with it swiftly in the Commons, leading to what could be a protracted political battle.
The plans would cut the number of peers almost in half, from 800 to 450. Mainly elected, they would serve 15-year terms, on a pay of £300 a day, less than the £60,000-a-year salary originally proposed.
The Prime Minister is also allowed to put up to eight unelected ministers from his Government into the second chamber.
Ministers insisted yesterday that the Commons would remain the main centre of legislative power, even when the public was free to vote for the members of both chambers.
And despite the radical cut in numbers, there will be no long-term savings from the changes.
One estimate even suggested that the new look chamber could cost taxpayers more .