The current text of the draft Withdrawal Agreement, which May presented to her Cabinet last week, states the transition period may be extended once to an ambiguous date of "20XX".
UK Prime Minister Theresa May announces outside 10 Downing Street that she has the support of her cabinet for Britain's Brexit deal with the EU.
"We're not going to be distracted".
They are aiming for 48 letters of no confidence, the number needed for a vote under Conservative Party rules.
He added: "Regrettably, this is not the situation, therefore, in accordance with the relevant rules and procedures of the Conservative party and the 1922 committee this is a formal letter of no confidence in the leader of the party, the Rt. Hon".
"The intention is clear that if it were to happen it ought to be a test of opinion very quickly in order to clear the air and get it out of the way", he told BBC radio.
You Do the Math: Can May Get Her Brexit Deal Through Parliament?
Mark Francois, one lawmaker who has submitted a letter, said he expected some colleagues were taking soundings from local party members over the weekend before making a decision.
Asked what she will do if the vote is lost, May said: "There's a process that Parliament will go through".
Corbyn, on which way he would vote in such a referendum, said: "I don't know how I am going to vote, what the options would be at that time".
Labour leader Mr. Corbyn says his party, which has 257 MPs, will not support the deal.
"We won't agree the leaving part, the withdrawal agreement, until we have got what we want in the future relationship because these two go together". "It is the future relationship that delivers on the Brexit vote".
May said she wanted any Brexit transition, during which Britain will remain a member in all but name and voting rights, to have ended by the time of the next national election, due in 2022. "Of course it has been a tough week, actually these negotiations have been tough right from the start, but they were always going to get even more hard right toward the end when we are coming to that conclusion".
British media say there is a critical week ahead for the prime minister.
Raab insisted he still supports May and would back her in any potential leadership challenge against her.
Mrs May's deal faces the prospect of being voted down in the House of Commons given the fierce opposition to her withdrawal plan puts a majority in doubt.
Opposition Labour leader Jeremy Corbyn appeared on the same TV show before the PM in which he said that a second referendum on Brexit could be possible but not at present. "It will no longer be the case that European Union nationals, regardless of the skills or experience they have to offer, can jump the queue ahead of engineers from Sydney or software developers from Delhi", she said in her speech.