The bill returns to the House of Commons with the PM hoping to overturn 15 amendments made by peers in the House of Lords.
"I am trying to negotiate the best deal for Britain", she told MPs.
His resignation came hours before British Prime Minister Theresa May faces crunch votes in parliament and a potential showdown with pro-EU rebels in her ruling party over whether parliament can prevent a no-deal Brexit.
The most important is the Lords' plan to give Parliament a meaningful vote on the final Brexit deal.
'I have had the privilege to work with inspiring, dedicated people; to be touched by the appalling stories that some of those caught up in our criminal justice system have shared with me - both victims and offenders; and in a small way to bring some influence to bear to help make our society more just and more secure'. The government said it would not support that amendment.
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He remanded the case of A-B- back to Judge Stuart Couch in Charlotte, North Carolina, for further proceedings. Fifteen former immigration judges signed a letter calling Sessions' decision "an affront to the rule of law".
Conservative Remainer MP Sarah Wollaston told BBC Radio 4's Today program that she was "minded" to defy the government on the first of these amendments, which calls for parliament to get a "meaningful vote" on any final deal agreed between the United Kingdom and EU.
He also warned that Britain "would not be ready in time" for Brexit and called for a referendum on the terms of the final deal.
Earlier this year, Lee had called on the government to release its economic impact assessments of Brexit and suggested the government change tack in talks with the European Union, underlining the deep rifts in his party over the best way to manage Britain's exit. I am confident I can get a deal that allows us to strike our own trade deals while having a border with the European Union which is as frictionless as possible.
Despite depending on the votes of the 10 DUP MPs for her precarious Commons majority, there were signs of cautious optimism among ministers that they would get the numbers to see off the revolt. MPs will vote on this particular amendment this afternoon.
"But if the Lords amendments are allowed to stand, that negotiating position will be undermined".