LONDON (Reuters) – British Prime Minister Theresa May faced the prospect of defeat in a historic vote in parliament on her Brexit deal on Tuesday, leaving the country in limbo about its membership of the world’s biggest trading bloc, which has shaped its economy for decades.

May urged lawmakers on Monday to take a second look at her deal but parliament appeared set to reject the agreement in a voting session due to start at 1900 GMT.

May’s hopes of saving the plan will hinge on the scale of her loss: if she limits the size of the expected defeat, May will probably ask Brussels for more concessions in the hope of getting her plan through parliament in another vote.

But a humiliating outcome could force May to delay Britain’s scheduled departure from the EU on March 29 and potentially open up other options ranging from a second referendum to leaving the EU with no deal.

Dominic Raab, who resigned as May’s Brexit minister in November in protest at her plans, said it was time to prepare for a no-deal Brexit, something many employers fear could mean chaos for their businesses.

“It’s time for us, through this vote, to make clear not just that the current terms are unacceptable, but that we are not just throwing our hands up in the air,” he told BBC radio.

“We are going to leave on March 29.”

In Britain’s deepest political crisis for at least half a century, May and EU leaders swapped assurances on the withdrawal deal on Monday, but there was little sign of a change of heart among rebel lawmakers.

Many members of May’s own Conservative Party say her plan would give Brussels too much power, chiefly an agreed insurance policy to avoid the return of a hard border in Ireland.

The EU told May that it stood by commitments to find ways to avoid triggering the Irish “backstop”.

The Northern Irish Democratic Unionist Party, which props up May’s minority government, has said it will not back the deal.

May has warned that without her deal, no Brexit at all would be more likely than Britain leaving without a deal.

She has also said that a break-up of the United Kingdom could be the result of parliament voting against the agreement and warned her Conservative Party against allowing the left-wing opposition Labour Party to seize the initiative.

Labour leader Jeremy Corbyn is expected to call a parliamentary vote of no confidence in May if she loses Tuesday’s vote.

May has refused to budge over her deal despite criticism from all quarters. The agreement, which envisages close economic ties with the EU, has united the opposing sides of the debate — pro-EU lawmakers who see it as the worst of all worlds and Brexit supporters who say it will make Britain a vassal state.

With a ‘no deal’ Brexit the default option if May’s deal is defeated, some lawmakers are planning to try to pull control of Brexit from the government.

But though May is weakened, the executive has significant powers, especially during times of crisis, so it was unclear how parliament would be able to take control of Brexit.