Foreign Secretary William Hague has urged Tory MPs not to vote for a referendum on Britain's future in the European Union.
Mr Hague, one of the Cabinet's most prominent eurosceptics, warned against trying to stage a popular vote on the EU at a time of "profound economic uncertainty".
David Cameron is facing potentially the most dangerous rebellion of his premiership so far when the Commons votes on a referendum in backbench debate on Monday.
At least 61 Conservative MPs have now signed a motion calling for a referendum on whether the UK should remain in the EU, leave or renegotiate its membership, and some predict the total number of rebels could top 85.
Writing in The Daily Telegraph, Mr Hague stressed the Conservative Party remained committed to repatriating powers from Brussels, but said that a referendum was not the way to go about it.
"As a Conservative, I want to bring powers back from Europe, as we set out in our election manifesto," he said.
"But a referendum on Britain's membership of the EU, especially at this time of profound economic uncertainty, is not the answer.
"Nothing would do more to help our economic recovery than a resolution of the eurozone's difficulties, while its disorderly break-up would have a very serious impact on our economy."
He received welcome support from Tory former cabinet minister, Peter Lilley - seen as a hardline eurosceptic - who also cautioned against a referendum.
"If we are in the business of getting back powers from Europe ... then we have to go about negotiating that return of powers and you cannot do that through a referendum," he told the BBC Radio 4 Today programme.
"The opportunity will present itself when Europe comes to us and the eurozone countries want to change the treaty to shore up the euro with further integrationist measures.
"We will say then 'Well you need our support because you need the unanimous support of all the countries to change the treaty. So even though that doesn't affect us we will only give you our support if in return you return some powers to us."'
Mark Pritchard, secretary of the Tory backbench 1922 Committee, called on Mr Cameron to impose only a non-binding single-line whip in Monday's vote, which would allow MPs to back the motion without facing disciplinary action.
However Downing Street has made clear that the Prime Minister expected all Conservative MPs to oppose not only the referendum motion - triggered by a petition of more than 100,000 public signatures - but also two amendments tabled in the hope of finding compromise.
Meanwhile Labour leader Ed Miliband has warned Mr Cameron not to make concessions to the Tory eurosceptics in a bid the defuse the threatened revolt.
He told The Guardian that Labour's decision to oppose the call for a referendum meant the Government would not lose the vote in the Commons.
"That means Cameron has a responsibility to make sure he does not put the party interest before the national interest, and he does not play footsie with this huge phalanx of sceptics in the Tory party," he said.