Britain's House of Commons started a marathon two-day debate on its Brexit legislation on what has been called "Super Tuesday".
Prime Minister Theresa May was in the chamber as lawmakers embarked on a debate on the government's Exiting the European Union Bill.
It has earned the expression Super Tuesday because of the number of votes that will take place in a single day.
Opposition MPs had called for the debate to be spread over a longer period.
The bill paves the way for all EU law passed over more than 40 years to become British law when Britain ends its membership of the bloc next March.
In what is a nail-biting day for May, Members of Parliament will be voting on a series of amendments agreed in the unelected House of Lords.
Brexit supporters fear that some of the amendments aim deliberately to sabotage Brexit to keep Britain in the EU.
Ahead of the debate government Justice Minister Phillip Lee resigned saying the Parliament was being sidelined and that he could not support how Brexit was being delivered.
Brexit Secretary David Davis, opening the debate, David Davis, the Brexit secretary, is opening the debate said more than 1,000 non-government amendments have been debated, and hundreds of government ones.
He told MPs that when amendments have been made undermining the purpose of the bill, or undermining Brexit, the government will reject them.
Referring to the amendments from the House of Lords, Davis said: "I understand that the House of Lords wants to improve the bill in various ways, but the cumulative effect of these changes can sometimes make it impossible to deliver the smooth and orderly exit we want."
Hundreds of pro-Remain campaigners gathered outside the Houses of Parliament to demonstrate their feelings on EU membership.
Veteran Labor MP Frank Field said in the debate: Labor's that if MPs back the Lords' amendment the government will be going naked into the negotiating chamber.
Labour's shadow Brexit minister Matthew Pennycook denies that MPs backing a call by the House of Lords for the British Parliament to have a meaningful vote on a Brexit deal is not aimed at blocking Britain's exit from the EU.
The government has made a number of changes to minimize any impact of losses it suffers during voting sessions later Tuesday and again on Wednesday.
Two of London's leading national newspapers used their front pages Tuesday to signal their opinions on the debate.
The Daily Express banner headline read: "Ignore the Will of the People at Your Peril".
The red-top tabloid Sun's headline read: "Great Britain or Great Betrayal", adding in a commentary: "Rebel Conservative MPs could today destroy the Prime Minister, the government and the Brexit that the majority voted for".