MPs have begun what is expected to be a passionate Brexit debate as they scrutinise the bill that will transfer all existing EU laws into UK law before the formal departure.
The line-by-line debate in Parliament comes with 500 days to go until the 29 March 2019 exit date - and a day after Brexit Secretary David Davis confirmed MPs will get a take-it-or-leave-it vote on the final deal.
It comes as a parliamentary report warned of the "catastrophic" effect of failing to install a new customs system before the departure.
The report said its absence would risk vast business disruption, create huge queues at Dover and leave food rotting in trucks at the border.
Hundreds of amendments have been suggested by MPs for the EU (Withdrawal) Bill, which is separate from the bill on the final deal itself.
MPs will also consider a Labour bid to allow the European Court of Justice (ECJ) to maintain its role during a transition period.
MPs will continue to debate the Bill on Wednesday but major battles are expected later during the eight days of committee stage, with the schedule not yet confirmed.
Mr Davis confirmed on Monday any deal on citizens' rights, the so-called divorce bill and a transition period will only take effect if MPs and peers approve the new piece of legislation to put it into British law.
But he confirmed the UK will still leave the EU, without a deal, even if the proposed Withdrawal Agreement and Implementation Bill is rejected by MPs.
This week's debate gives MPs opportunities to air grievances on the terms of exit though no crunch votes are expected.
Potential Tory rebels who want a vote on the Brexit deal are expected to criticise the government's bid to change the bill to enshrine the formal exit date on March 29 2019.
Labour leader Jeremy Corbyn, in a speech in Birmingham, will address Brexit in a pre-Budget warning to Chancellor Philip Hammond to protect the economy from the fall-out of Britain's departure.
He will tell the Association of Colleges in Birmingham the Budget is an "an opportunity to break with" a record of government cuts and address Britain's "productivity crisis".
"A bad Brexit deal risks making existing weaknesses in our economy - low investment, low productivity and low pay - even worse," he will say.
"Brexit should instead give us the impetus to tackle our productivity crisis, which is making our country poorer.
"The answer lies in investment: in infrastructure, new technologies and people."
Prime Minister Theresa May acknowledged the "challenges" and impending "ups and downs" of Brexit on Monday in a speech to business leaders.
She urged the Lord Mayor's Banquet in the City of London to "embrace this period with confidence and optimism ... not grounded in some article of faith, but with a clear understanding of our strengths as a nation".