A Welsh Conservative MP has urged fellow Tory Eurosceptics to back Theresa May's "half-loaf Brexit" or risk wrecking the whole project.
The call came as the UK government published its long-awaited White Paper on future relations with the EU.
Monmouth MP David Davies told BBC Wales that members of the European Research Group (ERG) were "very, very angry" about the deal struck at Chequers.
But he urged them to "swallow their pride" and back Mrs May.
Boris Johnson and David Davis have led a string of ministers who have quit since Friday's cabinet meeting in protest at how closely the prime minister plans to follow EU rules and regulations after Brexit.
Mr Davies made his plea for unity in a letter to fellow members of the ERG - Leave-supporting Conservative MPs led by the arch-Eurosceptic Jacob Rees-Mogg.
Describing the Chequers proposal as a "half-loaf Brexit", Mr Davies said it was "a disappointment to all who dared to dream", but added: "It is still a Brexit and, just about, fulfils our manifesto commitment."
He said MPs on both sides of the Brexit divide faced a "gamble".
Leavers who try to stop the prime minister's "soft Brexit" risk wrecking the whole process of withdrawal and toppling the government, Mr Davies said.
On the other hand, the Monmouth MP claimed Remainers hoping to sink the prime minister's plans could push the UK closer towards a no-deal exit from the EU.
"There is no room for rebellions from either pro or anti-Brexit Conservatives ... now is the time for us to swallow pride and back the Prime Minister," he wrote.
'Blurring the red lines'
Meanwhile former Welsh Secretary David Jones - also an ex-Brexit minister - said he was "extremely concerned" by what was on offer.
He pointed to Theresa May's "red lines" on leaving the customs union and the single market, and ending the jurisdiction of the European Court of Justice in Britain.
"It does look, if the Chequers communique is anything to go by, that there's going to be some blurring of those red lines and that is going to be a matter of some concern," Mr Jones told the BBC's Daily Politics.
"I'm extremely concerned, because the country voted to leave the European Union, and leaving the European Union means no longer being part of the apparatus of the European Union, including the single market, customs union and the European Court of Justice.
"And I would be extremely concerned if we were to get anything much less than that."