The British government has been accused of breaching international law after it introduced legislation to overturn an EU treaty on Monday.
UK Foreign Secretary Liz Truss introduced the bill that dramatically changes the Northern Ireland Protocol, insisting that the change was vital to preserve peace in the province.
The government, along with unionists in Northern Ireland, claim that the Brexit Withdrawal Agreement struck with the EU in late 2020 is not functioning, harming businesses and causing discontent.
Ms Truss said it had created significant trade barriers between mainland Britain and Northern Ireland, and was inflicting heavy administrative costs.
She said the bill was a “reasonable and practical solution” to address problems such as “burdensome customs processes” and inflexible regulations.
The legislation would “support political stability” and end “the untenable situation” where Northern Ireland was treated differently to the rest of the UK.
“We can only make progress through negotiations if the EU are willing to change the protocol itself. At the moment they aren’t,” Ms Truss told Parliament.
“In the meantime, the serious situation in Northern Ireland means we cannot afford to allow the situation to drift.”
A pivotal part to the bill is Clause 15, which gives ministers sweeping powers to dismiss any part of the protocol they consider will cause major economic or political disruption.
British Prime Minister Boris Johnson defended the plan, claiming it was “not a big deal” and simply a bureaucratic change that was “a relatively trivial set of adjustments”.
Mr Johnson denied that it broke international law.
"Our higher and prior legal commitment as a country is the Belfast-Good Friday Agreement and to the balance and stability of that agreement," he said.
But Simon Coveney, Ireland’s Foreign Minister, said the bill would “deeply damage” relations between the UK, Ireland and the EU.
“UK government now proposing to set aside international law, reject a partnership approach, ignore majority in NI and deliberately ratchet up tension,” he tweeted.
Mr Coveney said the approach would create “instability and is no fix”.
Irish Prime Minister Micheal Martin said: “It’s very regrettable for a country like the UK to renege on an international treaty.
"It represents a new low point because the natural expectation of democratic countries like ourselves, the UK and all across Europe is that we honour international agreements that we enter into."
The protocol is “an international deal ratified by British Parliament and approved by the PM”, Mr Martin said.
Breaching it “goes to the heart of the issue of trust”.
European Commission Vice President Maros Sefcovic said the EU regarded the UK’s actions with “significant concern” and would consider what steps to take next.
Mr Sefcovic said the EU would restart infringement proceedings against the UK and consider further legal action to protect the integrity of the EU single market.
He said the access of Northern Ireland businesses to that single market was now “at risk”, while the UK’s action had undermined the trust necessary for the operation of its post-Brexit trade deal with Brussels.
“Unilateral action is damaging to mutual trust,” Mr Sefcovic said.
Most politicians in Northern Ireland's Stormont Assembly have signed a joint letter to Mr Johnson stating their opposition to the proposed legislation.
The letter has been signed by 52 of the 90 Members of the Legislative Assembly, representing Sinn Fein, the Social Democratic and Labour Party and the Alliance Party.
Sinn Fein Stormont leader Michelle O’Neill is among the signatories, but Democratic Unionist Party leader Sir Jeffrey Donaldson said that all unionist MLAs opposed the protocol.
In a tweet, Ms O’Neill described the “unilateral actions of Boris Johnson” as “utterly reckless”.
“It is clearly a breach of international law," she said. "The impact on our businesses and economy could be colossal.
"The pro-protocol parties have jointly written to Boris Johnson today to firmly reject his legislation and approach."
The letter to Mr Johnson from the 52 MLAs said they “reject in the strongest possible terms your government’s reckless new protocol legislation, which flies in the face of the expressed wishes of not just most businesses, but most people in Northern Ireland”.
“Whilst not ideal, the protocol currently represents the only available protections for Northern Ireland from the worst impacts of that hard Brexit.”
The MLAs said they shared the desire to see post-Brexit arrangements work as smoothly as possible, but the best way to achieve this was through engagement with the EU.
“It is clear that solutions are available and deliverable — as have already been delivered in the area of medicines — but this must be on the basis of trust and the rule of law, rather than law-breaking and unilateral abrogation of treaty obligations,” they said.
The MLAs said they strongly rejected Mr Johnson’s claim to be protecting the Good Friday Agreement.
“To complain the protocol lacks cross-community consent, while ignoring the fact that Brexit itself — let alone hard Brexit — lacks even basic majority consent here, is a grotesque act of political distortion,” they wrote.
“Your claims to be acting to protect our institutions are as much a fabrication as the Brexit campaign claims you made in 2016.
“We will resolutely oppose this reckless Bill and continue to promote post-Brexit solutions on the basis of trust and honesty.”
Mr Donaldson said: “I want to be clear that those parties do not represent unionism.
“They represent one side of this debate and this institution in the assembly can only be restored on the basis of a cross-community consensus. Majority rule will not cut it.
“That’s what unionists were told over all the years. You cannot in a divided society operate on the basis of majority rule.
“So, to the Alliance, the SDLP and Sinn Fein who have written this letter, they need to recognise that these institutions can only function with the consent and support of unionists.
“Not a single [unionist] assembly member elected here at Stormont supports the protocol and that issue needs to be dealt with and, in the absence of an agreement with the EU, then the UK government is right to act and we look forward to giving full consideration to this legislation.”
US Secretary of State Antony Blinken spoke with Ms Truss on Monday and encouraged the UK to continue good faith negotiations with the EU to reach a solution that preserves the gains of the Good Friday Agreement.
The protocol was introduced to make the border between Northern Ireland and the Irish Republic invisible, despite the latter being an EU member.
But it has effectively imposed checks and bans on some goods entering Northern Ireland from the rest of the UK.
London says the protocol has created unnecessary bureaucracy, damaging businesses and causing tension between the unionist and nationalist communities.
It could also lead to social unrest undermining the 1998 Good Friday Agreement, particularly during the coming marching season.
The local political situation has changed with Sinn Fein, who want a united Ireland, for the first time winning a majority in the Stormont government in May’s election.
Since then, the DUP, which lost three seats and its majority, has refused to take part in power-sharing. It also bitterly opposes the protocol.
To some extent, Monday’s legislation serves as an incentive for the DUP to agree to sit in government with Sinn Fein.
The law change has been introduced after 300 hours of talks between British and EU officials resulted in deadlock. London hopes the bill will pressure the EU into concessions.
But the move has prompted an angry response against Britain — traditionally respected as a stalwart for following rules — from several areas, including the US, some Conservative MPs and lawyers.
There has been disgruntlement over onerous customs paperwork, which the new legislation proposes to bypass with a simple “green lane” for goods for just Northern Ireland and a “red lane” for products going south and into the EU.
A key demand from Conservative Brexiteers has also been the removal of the European Court of Justice for arbitration of trade disputes, which the bill has agreed to do.
But the EU refuses to budge on the court issue and the matter could lead to a destabilising trade war between the bloc and the UK at a time of severe economic hardship.