Jeremy Corbyn has said he wants to see the terms of any Brexit extension offered by the EU before deciding which way to vote on Monday.
Meanwhile, Chancellor Sajid Javid has said the Government will push "again and again" for a general election if the opposition denies Mr Johnson a pre-Christmas election.
Mr Javid said the stalemate over Brexit had reduced Westminster to a "zombie parliament", and that it was now up to Labour to end the deadlock by agreeing to go back to the country.
With the Budget scheduled for November 6 having already been cancelled, the Chancellor suggested ministers would put other government business on hold until the issue was resolved.
"The Opposition have said, week after week, that if there is a delay of three months, which is what they requested through Parliament, then they will vote for a general election, so let's see if they keep their word," he told the BBC Radio 4 Today programme.
"And if they don't then we will keep bringing back to Parliament a motion to have an election - and we will keep doing that again and again.
"As for other parliamentary business, we'll have to wait and see what that is, and we will react to it at that time."
While some around Mr Corbyn back a snap election, many Labour MPs are bitterly opposed to a poll, fearing confusion over the party's position on Brexit will cost them at the ballot box.
Shadow home secretary Diane Abbott said they needed an "explicit commitment" that a no-deal Brexit was off the table before they would be prepared to back an election.
EU envoys to Brussels were due to discuss the length a third delay to Brexit on Friday, though officials said they would be reluctant to set a date because it could dictate the direction of political events in London.
According to a draft decision by the 27, which was seen by Reuters on Thursday evening, a delay would be granted "with the view to allowing for the finalisation of the ratification" of the divorce agreement sealed with Mr Johnson last week.
The draft text left the new Brexit date blank, but said the split could take place earlier if ratification was completed earlier - an idea known as "flextension", an amalgamation of the words "flexible" and "extension".
An EU official explained: "It's basically between a three-month flextension or a two-tier one."
Under the first idea, Britain would leave on January 31, three months after the current departure date, but earlier if it and the EU ratify an agreement before that.
The second one would include a second specific date when Britain could leave.