Boris Johnson is considering seeking an early general election if MPs wanting to block a no-deal Brexit defeat the government this week.
The BBC understands "live discussions" are going on in No 10 about asking Parliament to approve a snap poll.
Political editor Laura Kuenssberg said it could happen as soon as Wednesday but no final decision had been taken.
Tory ex-ministers are joining forces with Labour to stop the UK leaving the EU on 31 October without a deal.
Amid mounting speculation about an election, Mr Johnson is due to hold an unscheduled cabinet meeting at 17.00 BST and will also speak to Conservative MPs on Monday afternoon.
Expulsion threat
The prime minister has said the UK must leave the EU on 31 October, with or without a deal, prompting a number of MPs to unite to try to prevent the UK leaving without an agreement.
They are expected to put forward legislation on Tuesday to stop no deal under "SO24" or Standing Order 24 - the rule allowing MPs to ask for a debate on a "specific and important matter that should have urgent consideration".
Sources have told the BBC the bill would force the prime minister to seek a three-month extension until 31 January if no withdrawal deal has been passed by Parliament by 19 October - the day after the next EU leaders' summit.
Tory rebels have been warned that those who support the legislation face being expelled from the party and deselected.
But leading figures, including ex-cabinet minister David Gauke, have insisted that despite the threat, they will press ahead and - in their words - put the "national interest" ahead of their own.
A No 10 spokesman said it was treating this week's Brexit votes as an issue of confidence, which traditionally trigger a general election if the government loses.
There is not scheduled to be another general election until 2022.
Under the terms of the Fixed Terms Parliament Act, Mr Johnson would require the backing of two-thirds of the UK's 650 MPs to trigger an early poll this autumn.
Should this happen, the prime minister would be able to recommend the date of the poll - likely to be a hugely contentious issue - to the Queen.
If Parliament were dissolved on Friday then the earliest possible date for an election would be Friday 11 October. With polls normally taking place on a Thursday, 17 October is potentially the more likely earliest opportunity.
But those who back a negotiated Brexit deal, or want to remain in the EU, are concerned the PM could delay the poll to the start of November, after the UK has left the EU, making it impossible to stop a no-deal Brexit.
