May is battling for her political survival after announcing a negotiating plan that enraged eurosceptics in her Conservative Party, who see it as keeping Britain too closely tied to Brussels.

The size of the threat to her position should become clear on Monday when eurosceptic MPs put forward a series of proposals to toughen up the government’s customs legislation during a parliamentary debate.

May is not expected to be defeated on the amendments, and could even order her government to back some of the least controversial ones to neutralise the impact of the rebellion without watering down her exit plan.

But, if she chooses to fight and then sees a large number of her own party rebel, it would undermine her leadership and cast fresh doubt on whether she can deliver the Brexit plan agreed by her cabinet this month at her Chequers country residence.

The Chequers agreement, which is only a starting point for negotiations with the EU, has already led to the resignations of her Brexit minister David Davis and foreign secretary Boris Johnson, and the eurosceptic faction say it has to change.

“I suspect the Chequers deal is, in fact, dead,” Conservative lawmaker Bernard Jenkin told the BBC.

It has also been rejected by some in the pro-EU faction in her party, with former minister Justine Greening calling on Monday for a second Brexit referendum to end the stalemate in parliament over the best future relationship with the bloc.

May’s spokesman said there would not be a second referendum under any circumstances, and restated the prime minister’s position that the Chequers plan was the only way to deliver a Brexit that worked in the best interest of the country.

On Sunday, May attempted to face down would-be eurosceptic rebels by warning that if they sink her premiership then they risk squandering the victory of an EU exit that they have dreamed about for decades.

Business minister Greg Clark urged party members to get behind the prime minister’s plan: “When it comes to parliament I hope and expect that it will be persuasive that what is on offer will be good for the UK, it would be good for every part of the UK.”

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A party meeting last week looked to have snuffed out talk of a confidence motion challenging May’s leadership, which would require 48 Conservative MPs to initiate, and 159 to win.

But, fuelled by criticism from U.S. President Donald Trump and anger among grassroots party members, the sentiment against May has gained fresh momentum.

A ministerial aide became the ninth party member to resign their post in protest over the Chequers deal. Lawmaker Scott Mann quit on Monday, saying the plan would put him in conflict with his constituents by delivering a “watered down” Brexit.

Davis said he would not speak in the parliamentary debate but could back one of the rebel amendments. Changes to the parliamentary schedule meant the debate was expected to start at 1630 GMT, later than originally planned, with the first votes due around 2000 GMT.

The amendments to the Taxation (Cross-border Trade) Bill have been proposed by arch-eurosceptic Jacob Rees-Mogg. He said he did not expect the bill, or another bill on trade due to be debated on Tuesday, to be blocked outright by the 650-member parliament.

“I’m sure Theresa May does not want to split the Conservative Party and therefore she will find that the inevitable consequence of the parliamentary arithmetic is that she will need to change it (the Brexit policy) to keep the party united,” Rees-Mogg said.

“We’ll have an idea of the numbers, I suppose, at 10 o’clock on Monday evening.”

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