THE British government is under pressure to publish its full legal advice around proposals to overhaul the Northern Ireland Protocol.
Nationalist and republican parties have strongly attacked plans for new legislation to be introduced in Parliament today.
Secretary of State Brandon Lewis insisted it would not breach international law and would be "correct".
This has been challenged by Sinn Féin and the SDLP as well as Labour and the Liberal Democrats.
Sinn Féin president Mary Lou McDonald said Mr Lewis was "talking through his hat" while SDLP leader Colum Eastwood said the British government was "fooling nobody".
The bill will see the government move without the consent of the EU to change the terms of the international treaty in a bid to reduce the checks on the movement of goods across the Irish Sea. The EU has made clear that such a step would represent a breach of international law and could prompt retaliatory action.
Mrs McDonald insisted that the protocol is working.
"What the Tory government is proposing to do in breaching international law is to create huge, huge damage to the northern economy, to the Irish economy," she said.
"They propose to breach international law and are on an agenda of undermining, attacking and damaging the Good Friday Agreement."
Mr Eastwood said British Prime Minister Boris Johnson's own advisers "believe the protocol legislation will breach the agreement with the EU and the attempt by Brandon Lewis to suggest otherwise is fooling nobody".
"This legislation is an extraordinary act of bad faith from a government that has proved it can't be trusted and it will be people in the north and Britain that suffer," he said.
Liberal Democrat Northern Ireland spokesperson Alistair Carmichael MP said the refusal to publish the legal advice "looks like yet another attempt to cover up Boris Johnson’s repeated lies and law-breaking".
"The government must come clean and publish what legal advice was received and who from in full," he said.
"The public deserves full transparency over the legality of plans to rip up the Northern Ireland Protocol and risk a trade war with our closest neighbours."
There is also growing tension in Dublin over the plans with foreign affairs minister Simon Coveney expressing anger over "political gamesmanship".
He said relations between Ireland and Britain were "in a bad place" and accused his British counterpart Liz Truss of making no effort on Northern Ireland.
Meanwhile, a 51-year-old man will appear in court today charged with firearms offences in connection with a security alert that led to Mr Coveney being evacuated from a peace event. He is one of two men arrested by police on Wednesday. The other, well-known loyalist Winston Irvine, appeared in court on Saturday charged with firearm offences.
