Boris Johnson has warned he will abandon his Brexit bill if MPs do not approve a three-day timetable proposed for its debate.
The prime minister said if the timetable is rejected and the European Union confirms a delay to January or later, then the government will press for an election.
He told MPs if they vote against him, "that the Bill will have to be pulled and we will have to go forward to a General Election".
The prime minister is trying to avoid that outcome by urging MPs to back his Withdrawal Agreement Bill (WAB), which was published on Monday night, in a Commons debate set to conclude with two crucial votes around 7pm.
MPs are debating the WAB second reading and whether to approve the three-day timetable proposed for debate to allow its passage through parliament.
Under the Fixed-term Parliaments Act the prime minister would need a two-thirds majority in the Commons to successfully call a snap election.
A Number 10 source revealed Mr Johnson will call EU leaders after Tuesday evening's debate to reiterate the government still plans to leave the EU at the end of October and "no delays should be offered".
The source added: "If EU accepts PARLIAMENT's request for delay to Jan then as the PM has made clear in the house we pull bill and General Election (sic)."
The WAB is the detailed legislation relating to Mr Johnson's Brexit agreement, which, if passed will see the deal enshrined in UK law.
Mr Johnson told MPs that if they back the bill they "can get Brexit done and move our country on".
But Labour leader Jeremy Corbyn stressed to his MPs they must not back the "rotten deal".
"We will be voting against the second reading tonight, and if that is carried we will be voting against the programme motion," he said.
He accused the PM of "trying to blindside" parliament with a "disgraceful attempt to dodge accountability, scrutiny, and any kind of proper debate".
He added that the deal "fails to protect our rights and our natural world, fails to protect jobs and the economy, fails to protect every region and every nation in the United Kingdom".
Labour's chief whip Nicholas Brown offered an olive branch to the PM, by telling him he was "available at any point to seek a consensus with you on a programme motion that would command the support of all sides of the House".
He was proposing that Labour and the government agree on a more appropriate timetable that will allow proper scrutiny of the deal, before giving MPs a chance to agree on it.
In a letter to the Prime Minister, he added: "No parliamentarian seeking to properly scrutinise and improve such a vital piece of legislation could agree to support the Government's proposed programme motion."
If everything goes the prime minister's way, MPs will have given approval to his WAB, in principle, and they will have agreed to conclude the debate on it within a mere three days.
If things don't go his way, the UK could be looking down the barrel of a no-deal Brexit in little over a week's time, as Mr Johnson would say, if MPs reject his deal.
However, pro-EU MPs who vote against the prime minister on Tuesday will say the result makes an extension more likely, with the EU confirming earlier it could allow a delay if MPs reject the PM's proposal.
The first vote on Tuesday will be on the Bill’s “in principle” second reading - the first opportunity for MPs to debate the main principles of the Bill.
Ministers have insisted they are confident they have the numbers to get the WAB through the Commons, despite their defeat in Saturday’s special sitting.
But, with no Commons majority, Mr Johnson faces a major battle to achieve his pledge to lead the country out of the EU by the October 31 deadline.
If the Bill gets through its second reading, the government will need MPs to approve a “programme motion” - the second vote of the day - which will set out a three-day timetable for its passage through the Commons.
If MPs do approve such a swift debate, it could pave the way for the Lords to consider it over the weekend, ready for the Bill to receive its royal assent at the start of next week.
But many MPs are deeply unhappy that there is so little time for detailed scrutiny of a such an important Bill, which runs to 110 pages with another 124 pages of explanatory notes.
However, Leader of the House Jacob Rees-Mogg warned on Monday the programme motion was essential if they were to meet the Halloween deadline.
“People who do not vote for the programme motion will not be voting for Brexit on October 31,” he said.
Failure to get the motion through would open up the prospect that Mr Johnson will be forced to accept another lengthy delay to Britain’s departure – something he has vowed not to do.
If the PM wins both votes, under the proposed timetable, the Bill would then move to the committee stage – which will continue on into Wednesday – when MPs will have the opportunity to put down amendments.
- Read the Withdrawal Agreement Bill in full:
These are expected to include attempts to keep the UK more closely aligned with the EU through a customs union and to stage a second referendum, two amendments Labour has already said it will push for.
Number 10 is opposed to a customs union and second referendum, and warned that if the legislation in the Commons “steps too far away” from what has been agreed with the EU then it would “bring into question ratification”.
EU chief negotiator Michel Barnier told the European Parliament that "this is the only possible agreement", signalling it is the last deal any PM can broker.
But European Council president Mr Tusk suggested another extension to Article 50 could be granted as he consults EU leaders over the requested delay and MPs prepare to debate the WAB.
He said European Union leaders "will decide in coming days" whether to grant Britain another extension to the Brexit deadline, but that the decision depends on developments in London.
Jean-Claude Juncker said it has "pained" him to spend so much time dealing with Brexit, which he described as "a waste of time and a waste of energy".
The new Brexit deal must also win backing from the European Parliament, if it is to be ratified, but its Brexit co-ordinator, Guy Verhofstadt, suggested "all problems faced by EU27 nationals in the UK need to be solved" first.
Ahead of the debate, Mr Johnson called on MPs to get behind the agreement, warning that the public did not want any further delay.
“We have negotiated a new deal so that we can leave without disruption and provide a framework for a new relationship based on free trade and friendly co-operation,” he said in a statement.
“We are leaving the European Union but we will always be European.
“The public doesn’t want any more delays, neither do other European leaders and neither do I.
"Let’s get Brexit done on October 31 and move on.”
Meanwhile, judges at Scotland’s highest civil court, who have been asked to rule on whether the PM lawfully complied with the Benn Act, delayed making a decision until it becomes clear to them it was “complied with in full”.
Under the Benn Act, which was passed by MPs trying to fend off a no-deal Brexit, Mr Johnson was forced to send an unsigned letter to Brussels requesting an extension to the October 31 deadline because MPs did not support his deal on Saturday.
But he signed a second letter saying a delay would be a mistake.