Theresa May is facing a second Brexit defeat in the House of Lords within a week, putting her under further pressure as she attempts to meet her end-of-March Article 50 deadline.
Peers are expected to back a demand - supported by former deputy prime minister Michael Heseltine - for a vote in both Houses of Parliament on the terms of the deal for the UK leaving the EU.
Last week, after a turbulent and at times bad-tempered debate, the Lords voted by 358-256, a majority of 102, in favour of an amendment demanding protection for EU citizens living in the UK after Brexit.
That has already triggered Parliamentary "ping pong", since the Government has vowed to overturn the amendment - and any others passed in the Lords - so the Article 50 Bill can become law unamended.
But the Government's opponents in the Lords are confident of victory in a vote on a new clause headed: "Parliamentary approval for the outcome of negotiations with the European Union".
The new clause proposes:
:: The Prime Minister may not conclude an agreement with the European Union under Article 50(2) of the Treaty on European Union, on the terms of the United Kingdom's withdrawal from the European Union, without the approval of both Houses of Parliament.
:: Such approval shall be required before the European Parliament debates and votes on that agreement.
:: The prior approval of both Houses of Parliament shall also be required in relation to an agreement on the future relationship of the United Kingdom with the European Union.
:: The prior approval of both Houses of Parliament shall also be required in relation to any decision by the Prime Minister that the United Kingdom shall leave the European Union without an agreement as to the applicable terms.
When the same new clause was debated in the Commons, the Brexit Minister David Jones told MPs: "I can confirm that the Government will bring forward a motion on the final agreement, to be approved by both Houses of Parliament before it is concluded.
"We expect and intend that this will happen before the European Parliament debates and votes on the final agreement."
But Labour, backed by Liberal Democrat peers, crossbenchers and a handful of Tory rebels led by Lord Heseltine, are determined to get the Government's pledge for what they call a "meaningful vote" written into the Bill.
Labour's leader in the Lords, Baroness Smith, said: "I have said all along that we would not block Brexit while reserving our right to challenge and scrutinise any legislation put before us.
"As we showed last week, we may also pass amendments on issues where we think it would be helpful for both the government and the Commons to take another look."
With the Prime Minister vowing to trigger Article 50 before the end of March, senior peers now expect "ping pong" on Monday 13 March, with the Lords amendments being debated - and thrown out - by MPs in the Commons in the afternoon.
The bill would then return to the Lords in the evening of the same day, when peers are expected to call a halt to their demands for changes and allow the legislation to reach the statute book.
Mrs May said: "I'm very clear we're putting this bill through Parliament."
She added: "We're doing this because on 23 June last year, the British people voted for the UK to leave the EU - this bill will enable us to start the process of negotiations for use to leave the EU."
In another twist to the Brexit drama being played out in Parliament, the Prime Minister has been warned not to use her Great Repeal Bill to avoid full scrutiny of the Brexit process.
The House of Lords Constitution Committee has said she must not use the legislation to "pick and choose" which elements of European law she wanted to scrap or alter without Parliament's full involvement.
The Prime Minister has said the Great Repeal Bill will scrap the European Communities Act, ending the legal authority of EU law.
The committee said the bill was "likely to involve a massive transfer of legislative competence from Parliament to Government".
Committee chairman Lord Lang, a Cabinet minister under John Major, said the Government might need to be given "wide-ranging powers" over the process of turning EU legislation into domestic law.
"Those powers should not, however, be used to pick and choose which elements of EU law to keep or replace - that should be done only through primary legislation that is subject to proper Parliamentary scrutiny," he said.
Liberal Democrat leader Tim Farron said Mrs May was "playing with fire" over the Repeal Bill.
"If the Government has found the Article 50 Bill difficult, they should be under no illusion - this will be hell.
"For all Theresa May's talk of giving power to the people she is increasingly fighting to ensure that the whole Brexit process occurs behind closed doors with only her inner circle having any say."
The Archbishop of Canterbury has said a second referendum on Mrs May's final Brexit deal would bring more division to an already divided country.
The Most Reverend Justin Welbby said: "Division of our country is not a mere fact to be navigated around like a rock in a stream, but something to be healed, to be challenged and to be changed."
"On this amendment, I fear I believe we risk making the process too complex and the substance too simple."