Two senior Conservatives from the Leave and Remain wings of the party have come together to urge Tory MPs to back Theresa May in a series of crunch Commons votes on Brexit.
However in supporting the PM, former home secretary Amber Rudd, a leading Remain supporter, and ex-party leader Iain Duncan Smith, a long-standing Brexiteer, warned defeat could lead to the fall of the Government.
It raises the stakes ahead of potentially defining week in Westminster for Mrs May's premiership.
In a joint article for The Sunday Telegraph, Ms Rudd and Mr Duncan Smith said voting to overturn or water down a series of amendments inserted by the Lords into the EU (Withdrawal) Bill should be a “no brainer”.
They said Labour would be quick to exploit any setback for the Government for their own purposes.
“Jeremy Corbyn will do everything he can to stop us,” they warned.
“That includes cynically trying to frustrate the Brexit process for his own political ends, as he will try to do next week when the Commons votes again on the EU (Withdrawal) Bill.
“So it behoves us all to demonstrate discipline and unity of purpose in support of the Prime Minister.
“We cannot allow ourselves to become divided and risk losing the precious chance to go on implementing policies that transform lives.”
Ministers – who have accepted just one of the 15 amendments to legislation – are confident of winning most of the votes when the bill returns to the Commons on Tuesday and Wednesday.
However, pro-EU Tory rebels believe they could be vulnerable on key measures including the customs union and a requirement for Parliament to have a decisive say over what happens next if it rejects a final Brexit deal.
With the Government dependent on the DUP for its majority, Tory whips are expected to crank up the pressure on potential rebels to ensure they have the numbers when it comes to the divisions.
They may be boosted by support from a handful of pro-Brexit Labour MPs.
Former deputy prime minister Damian Green wrote in the Sunday Express that the majority of the crucial votes would “pass easily”.
He said: “The Westminster air is again full of the scent of rebellions, chaos and catastrophic Government defeats.
“I predict they simply won’t materialise for one simple reason: the whips can count.
“If they think that the Government won’t have a majority, they advise a change in policy.”
Theresa May, in Quebec for the G7 summit, denounced the unelected peers who passed the amendments, accusing them of going far beyond their role as a revising chamber.
“Let’s remember what the Withdrawal Bill is for: it’s about delivering a statute book that is ready for Brexit day,” she said.
“Of course, the Lords has a revising role to play – but some of the amendments that were passed and the comments that were made went far beyond that.
“You had peers talking about stopping Brexit or trying to tie the Government’s hands in the negotiations.
“This Government is delivering on the decision made by the country in the referendum to leave the EU and we will not accept anything that prevents us from taking back control of our money, laws and borders.”
In their article, Ms Rudd and Mr Duncan Smith said the bill was not about competing visions of the future, but a “technical measure” to ensure there was “legal certainty” when Britain left the EU in March 2019.
“The disagreements in the party do not extend to whether we should leave, only how we do it,” they said.
“So for Conservatives of every outlook, givingour full support to the Government this week should be a no-brainer. The House of Commons backed the Withdrawal Bill at third reading with a clear majority. Not a single Conservative voted against it.”
For Labour, shadow Brexit secretary Sir Keir Starmer said pro-EU Tory MPs had a chance to alter the direction of the negotiations if they voted with the opposition on the key amendments.
“If Tory MPs who care about these amendments vote with us there is a real chance for Parliament to change the course of the Brexit negotiations and bring some order where there is real chaos,” he told BBC One’s The Andrew Marr Show.