Theresa May's plans for Brexit will face their first Commons hurdle as MPs vote on the Bill allowing her to start divorce proceedings with Brussels.
The legislation giving the Prime Minister permission to trigger Article 50 is expected to pass its first test, with Labour leader Jeremy Corbyn ordering his MPs to back the Government's Bill.
But a revolt from pro-Remain MPs on the Labour benches could give him a headache and he may be forced to sack frontbenchers who fail to follow his orders.
Meanwhile, the UK's former ambassador to the European Union will give evidence to MPs following his shock resignation from the diplomatic post.
Sir Ivan Rogers will be quizzed about UK-EU relations in preparation for Brexit after using his resignation message to staff in the Brussels mission to urge them to challenge "ill-founded arguments and muddled thinking".
In the Commons chamber, the European Union (Notification of Withdrawal) Bill will be voted on by MPs at the end of a second day of debate.
On Tuesday, MPs spoke until midnight after Brexit Secretary David Davis introduced the legislation by stressing the Government's determination to trigger Article 50 by the end of March, starting the formal two-year countdown to leaving the EU.
The Government was forced to seek Parliament's approval for its plans by a Supreme Court ruling last week.
But Mr Davis warned MPs they would not be able to vote to block Brexit, telling them the "point of no return" had already passed.
Following the vote for Brexit in last June's referendum, Mr Davis said the only question now before Parliament was: "Do we trust the people or not?"
The Government faces an additional hurdle after Commons Speaker John Bercow selected a Scottish National Party amendment which would delay Article 50 on grounds including that the Government has failed to provide for consultation with devolved administrations or published a White Paper on its negotiating strategy.
But ministers remain confident that the legislation will be fast-tracked through Parliament in order to meet Mrs May's deadline for triggering Article 50.
Mr Corbyn has been struggling to contain a revolt against his decision to impose a three-line whip ordering Labour MPs to vote for the Bill, with shadow ministers Jo Stevens and Tulip Siddiq quitting in protest and other frontbenchers threatening to oppose it even if it costs them their jobs.
During the debate on Tuesday, Catherine West said she would join the Labour rebels, putting her shadow Foreign Office role on the line.
The Hornsey and Wood Green MP said her concerns were "not just about jobs and the economy" but the issue was also about "our children, our grandchildren and about peace and prosperity".
Jeff Smith and Thangam Debbonaire, who as whips are meant to enforce party discipline, have indicated they would rebel in the vote as has shadow transport minister Daniel Zeichner.
But the real parliamentary battle is not expected to take place until next week, when opposition parties attempt to push through a series of amendments as the Bill undergoes detailed scrutiny in its committee stage.