The Government says that its 58-page Internal Market Bill will protect jobs and trade across the UK when the Brexit transition period ends in December.
It is highly technical legislation which sets out rules for the operation of the UK internal market.
Westminster says it will enable the Government "to provide financial assistance to Scotland, Wales and Northern Ireland with new powers to spend taxpayers' money previously administered by the EU".
A primary objective is to empower ministers to pass regulations on state aid and trade even if they run contrary to the Northern Ireland protocol that was previously agreed between London and Brussels.
The bill states that "special regard" must be given to Northern Ireland's place in the UK internal market and that there should be no new checks on goods moving from Northern Ireland to Britain.
Ministers have the power to modify or "disapply" rules that come into force from the start of next year if the UK and the EU are unable to come to alternative arrangements through a trade deal.
The Prime Minister told MPs yesterday that his priority was to preserve the Good Friday Agreement and the peace process.
"To do that we need a legal safety net to protect our country against extreme or irrational interpretations of the protocol which could lead to a border down the Irish Sea in a way, that I believe, would be prejudicial to the interests of the Good Friday Agreement and prejudicial to the interests of peace in our country," Boris Johnson said.
The DUP has given a cautious welcome to the bill but believes it still falls significantly short of addressing unionist concerns.
There is staunch opposition from Northern Ireland's four pro-Remain parties. Deep unease has also been expressed among some senior Tory MPs that the UK is abandoning its support of the principles of international law.
Given the size of the Government's majority, the bill should likely pass through the Commons. But a legal challenge seems inevitable.
Former Supreme Court justice, Lord Sumption, told the BBC: "There may be a political justification … but there's no way in which this can be consistent with the legal obligations of the Government under treaty. And the Government has cheerfully admitted that."