The row threatens to disrupt already tough post-Brexit trade negotiations, fuelling growing fears of failure that would see more than four decades of EU-UK integration come to a crashing halt at the end of this year. "It should be an absolute final resort, so I do have misgivings about what is being proposed", said the former Tory leader, who famously broke his own word that he was not step down as Prime Minister if he lost the 2016 European Union referendum, reportedly telling aides: "Why should I do all the hard s**t?"
The Internal Market Bill, which the government hopes to pass into law within weeks, would give the British government the power to override the EU's agreed role in oversight of trade between mainland Britain and Northern Ireland.
But EU leaders have dismissed this as "spin" and warned Johnson to uphold commitments he himself made in the Brexit treaty previous year - demanding he withdraw the offending parts of the new bill by the end of September.
During a five-hour debate ahead of the vote on Monday evening, Johnson claimed the EU's current approach could lead to excessive checks and even tariffs on goods moving from Great Britain to Northern Ireland.
"Breaking global law is a step that should never be taken lightly", wrote Tory MP and former chancellor Sajid Javid in a statement, adding that he could not support "pre-emptively reneging" on the withdrawal agreement and that he would not be supporting the bill on its second reading on Tuesday. All of Britain's living former prime ministers have expressed concern about his plan as have many senior figures in his Conservative Party. Both sides accepted the compromise to protect the open border, which helps underpin the peace process in Northern Ireland.
He told BBC Radio 4's Today programme: "The proposition that we should march through the Lobby as lawmakers and say that we are going to ignore and disavow a law that we have passed, to do with the rule of law, that is completely unacceptable".
"That illusion must be decently despatched".
The bill is created to enable goods and services to flow freely across England, Scotland, Wales and Northern Ireland when the United Kingdom leaves the EU's single market and customs union on January 1 at the end of the current transition period. That was agreed through the Northern Ireland protocol that could have resulted in an effective border down the Irish Sea if a trade deal was not reached.
But opposition Labour spokesman Ed Miliband ridiculed this suggestion, saying: "Either he wasn't straight with the country about the deal in the first place or he didn't understand it".
He added: "This is his deal".
Rehman Chishti, the MP for Gillingham and Rainham in Kent, said he was quitting as the government's special envoy for freedom of religion.
MPs will begin detailed line-by-line scrutiny of the Bill on Tuesday, with votes expected next week on amendments to the Northern Ireland provisions which some Tories may back.
Even some Brexit-backing Tories are unhappy, with one, Charles Walker, saying: "I'm no fan of the European Union. but surely we have to exhaust all other options before we press the nuclear button".