LONDON (AP) — In their first weekend session in 37 years, British lawmakers in Parliament debated whether to accept Prime Minister Boris Johnson’s proposed new divorce deal with the European Union. It’s a momentous decision — but one that they still may not get resolved on this day.

First they will vote on whether — yet again — to delay their decision on Brexit.

Johnson implored legislators to ratify the deal he struck this week with the bloc’s 27 other leaders. He said members of the House of Commons should “come together as democrats to end this debilitating feud” over Brexit, which has bitterly divided the country since British voters narrowly chose in a 2016 vote to leave the EU.

“Now is the time for this great House of Commons to come together… as I believe people at home are hoping and expecting,” Johnson told lawmakers.

But he may not get the vote he craves.

As the session of Parliament opened, House of Commons Speaker John Bercow said he would first allow a vote on an amendment that puts the vote on the deal off until another day. Those behind the amendment say it will remove the risk that the U.K. could stumble out of the bloc without a deal on the Oct. 31 deadline — a prospect that economists say would disrupt trade and plunge the economy into recession.

The amendment makes support for the deal conditional on the legislation to implement it being passed by Parliament, something that could take several days or weeks.

One of the lawmakers behind the measure, Oliver Letwin, said it would prevent the U.K. from leaving at the end of the month “by mistake, if something goes wrong during the passage of the implementing legislation.”

It would also give lawmakers another chance to scrutinize — and possibly change— the Brexit departure terms while the legislation is passing through Parliament.

If this amendment passes, Johnson will have to ask the EU for a delay to Britain’s departure date. Last month Parliament passed a law compelling the government to do that if no deal is approved by Saturday.

The prime minister signaled that he would do that, but under duress. He is compelled by law to ask for the extension, but he said “it cannot change my judgment that further delay is pointless, expensive and deeply corrosive of public trust.”

And he warned Saturday that the bloc’s approval could not be guaranteed.

“There is very little appetite among our friends in the EU for this business to be protracted by one extra day,” Johnson said. “They have had three and a half years of this debate.”

French President Emmanuel Macron made the same point a day earlier in Brussels, when he was asked whether he would support an extension to the deadline in case British lawmakers rejected Johnson’s Brexit proposal.

“I want us to finish this off and speak about the future,” Macron said. “The Oct. 31 date must be respected. I don’t believe new delays should be granted.”

The EU’s budget commissioner, Guenther Oettinger, was quoted Saturday as telling Germany’s Welt am Sonntag newspaper that if British lawmakers reject Johnson’s deal, the U.K. is likely to crash out of the bloc with no deal.

Brexit Secretary Stephen Barclay urged lawmakers to reject the amendment.

“It would cause further delay when our constituents and our businesses want an end to uncertainty and are calling for us to get this done,” he said.

If the amendment passes, Britain could still leave the EU on Oct. 31, if Parliament approves the legislation — the Withdrawal Agreement Bill — in time. The government plans to introduce the bill early next week and could hold late-night sittings of Parliament in hope of getting it passed within days.

As lawmakers gathered inside Parliament — their first Saturday sitting since the 1982 Falklands War — tens of thousands of anti-Brexit demonstrators gathered in London for a march on the building, demanding a new referendum on whether Britain should leave the EU or remain.

“I fervently believe that we should remain in the EU,” said Bruce Nicole, an Anglican vicar from Camberley, south of London, who attended the protest. “I am British but I am also European. I don’t believe the current deal offers any benefits at all.”

Since striking a deal with the EU on Thursday, Johnson has been both imploring and arm-twisting Conservative and opposition lawmakers alike as he tries to win majority support for his deal.

Johnson’s Conservative Party holds only 288 seats in the 650-seat House of Commons, so he will have to rely on support from other parties and independent lawmakers to get over the line.

The result looks set to be close, although Johnson has had some success winning over both hard-core Conservative Brexiteers and a handful of opposition Labour lawmakers who represent pro-Brexit parts of the country.

Johnson hopes for success in getting a fractious Parliament to back the deal after his predecessor, Theresa May, failed three times to get lawmakers behind her Brexit plan.

Yet his hopes of getting the deal through Parliament were dealt a blow when his Northern Ireland ally, the Democratic Unionist Party, said it would not back him. The party says Johnson’s Brexit package — which carves out special status for Northern Ireland to keep an open border with EU member Ireland — is bad for the region and weakens its bonds with the rest of the U.K.

“We will not be supporting the government, we will be voting against,” said the party’s deputy leader, Nigel Dodds. “Because it isn’t Brexit for the whole of the United Kingdom.”

To make up for the votes of 10 DUP lawmakers, Johnson has tried to persuade members of the left-of-center Labour Party to support the deal. Late Friday the government promised to bolster protections for the environment and workers’ rights to allay Labour fears that the Conservative government plans to slash those protections after Brexit.

Labour leader Jeremy Corbyn dismissed those promises as inadequate.

“This deal is not good for jobs, damaging for industry and a threat to our environment and natural world,” he said. “Supporting the government this afternoon would merely fire the starting pistol in a race to the bottom in regulations and standards.”

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