Prime Minister Theresa May faces a showdown on Tuesday with lawmakers who want power to force her government to go back to the negotiating table if they reject a Brexit deal, testing her plans for leaving the European Union.

Officials from May’s Conservative Party have been lobbying lawmakers to reject amendments handed down from the upper house of parliament on her Brexit blueprint, the EU withdrawal bill.

On Tuesday, parliament will debate a demand for a “meaningful vote” on any agreement May negotiates with Brussels before leaving the bloc next March.

Hours before the debate started, a justice minister who has long been critical of the handling of Brexit, resigned in protest at what he called the government’s “wish to limit” the role of lawmakers in shaping Brexit and said he would vote against the prime minister.

May and her ministers renewed appeals for unity, after the government appeared to have secured a compromise to quell a potential rebellion on Wednesday over Britain’s trading ties with the EU.

The government is most vulnerable on the issue of a “meaningful vote”. An amendment approved by the House of Lords, the upper house, could mean sending May back into negotiations with the EU just months before Britain is due to leave if lawmakers reject a Brexit deal.

The government says that would undermine its negotiating position in talks to leave the bloc and Brexit minister David Davis warned lawmakers the government would never allow them to reverse Brexit.

“Whatever we do, we’re not going to reverse that,” Davis told BBC radio. “A meaningful vote is not the ability to reverse the decision of the referendum.”

May, who lost her party’s majority at an ill-judged election last year, made a last-ditch appeal to lawmakers on Monday and Davis sent a letter making the same case – vote against the government and risk tying Britain’s hands in the Brexit talks.

The government has also tried to stem rebellions by offering its own options – on the “meaningful vote”, it has proposed a 28-day breathing space if parliament rejects a Brexit deal. Within that period, the government would have to make a statement on its plans.

It is not clear whether that will win over potential rebels.

Senior pro-EU Conservative lawmaker Dominic Grieve tabled his own competing amendment which could force ministers to hand over control of its Brexit strategy to parliament if there is no deal by mid-February. The government said it would not support that amendment.

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