MPs are to begin two days of debate over the government’s parliamentary bill to get the formal process of Brexit under way.
Discussions on the European Union Bill have been extended to midnight on Tuesday to accommodate more speakers, with a vote to take place on Wednesday.
Labour leader Jeremy Corbyn has ordered his MPs to vote with the government, but some are expected to defy him.
Ministers want to get the bill passed in time to trigger Brexit by 31 March.
The European Union (Notification of Withdrawal) Bill would allow Prime Minister Theresa May to invoke Article 50 of the Lisbon Treaty, getting official talks between the UK and the EU started.
The Liberal Democrats and Scottish National Party are to vote against it, but Labour’s leadership is backing it, meaning the government is expected to win.
The size of the Labour rebellion will be closely scrutinised, with several of his MPs indicating they plan to defy Mr Corbyn.
Two shadow ministers have quit, saying they want to vote against it.
Former Conservative Chancellor Ken Clarke has also said he will vote against the bill.
If the vote goes the government’s way, the bill will return to the Commons next week for the committee stage when opposition parties will try to push through a series of amendments.
Speaking in Dublin on Monday, Mrs May said MPs would face a very clear choice when they came to vote on the bill.