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 the wider Conservative parliamentary party later.
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 across party lines 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 – including former ministers and prominent backbenchers – have been warned that those who support the legislation face being expelled from the party and deselected.
But leading figures, including ex-Justice Secretary David Gauke, have insisted that despite the threat, they will press ahead and – in their words – put the “national interest” ahead of their own.