The UK's relationship with the EU has been plunged into crisis after ministers rejected a demand by Brussels to drop plans to override key elements of the Brexit withdrawal agreement.
London's proposals to change key parts of the deal relating to Northern Ireland do not protect the Good Friday Agreement as the Government says - they do the opposite, the EU claimed.
At a stormy meeting in London, European Commission vice-president Maros Sefcovic gave the UK until the end of the month to drop the provisions in the Internal Market Bill or face the potential collapse of talks on a free trade agreement.
However, Cabinet Office Minister Michael Gove, who co-chairs a joint committee on the withdrawal agreement with Mr Sefcovic, said the Government was not prepared to back down.
"I explained to vice-president Sefcovic that we could not and would not do that," Mr Gove told reporters following the meeting.
"I made it perfectly clear to vice-president Sefcovic that we would not be withdrawing this legislation. He understood that. Of course he regretted it."
The emergency talks were called after ministers admitted on Tuesday that provisions in the Bill to enable the Government to change elements of the withdrawal agreement relating to Northern Ireland would breach international law.
In a strongly worded statement following the meeting, the European Commission said Mr Sefcovic had made clear that the British proposals had "seriously damaged trust" between the two sides and that it was up to the UK to repair the relationship.
It said he had made clear that the EU would "not be shy" in using the "mechanisms and legal remedies" contained in the agreement to address any violations if the UK did not withdraw the provisions.
"Violating the terms of the withdrawal agreement would break international law, undermine trust and put at risk the ongoing future relationship negotiations," the statement said.
"The EU does not accept the argument that the aim of the draft Bill is to protect the Good Friday Agreement. In fact, it is of the view that it does the opposite.
"Vice-president Maros Sefcovic called on the UK Government to withdraw these measures from the draft Bill in the shortest time possible and in any case by the end of the month."
Mr Gove denied the Government was seeking to set aside the withdrawal agreement or to shirk from the protocol on Northern Ireland which means that some goods entering from the rest of the UK will be subject to EU tariffs.
"We are absolutely serious about the implementation of the protocol," he said
"But we have to ensure the protocol is implemented in a way that respects the fact that Northern Ireland is an integral part of the United Kingdom and part of our customs territory. It is British ministers in Westminster who are responsible for good governance in Northern Ireland."
Mr Gove said he still hoped the two sides could resolve their differences through the joint committee, but he refused to be drawn on the prospects of a deal being reached.
"It is not for me to speculate about the chances for success. It is my job to work for success," he said.
The row erupted as the EU and UK chief negotiators, Michel Barnier and Lord Frost, were concluding the latest round of talks on the post-Brexit relationship, including a free trade agreement, in London.
Taoiseach Micheal Martin repeated yesterday that he was not optimistic that a UK-EU trade deal would be reached, raising the prospect of high tariffs on Irish exports to its neighbour.
Mr Martin said he told Prime Minister Boris Johnson the move would be "very unsettling" for Northern Ireland.
"I pointed out very strongly to him that this was very unsettling for Northern Ireland, that it was dragging Northern Ireland back into the centre stage, that it was bad for Northern Ireland politics and that it would be divisive," Mr Martin told RTE One's Morning Ireland.
"I made a point to him that we all have obligations as political leaders to protect our peoples from the worst effects of a no-deal, and that this intervention was very serious and had raised a fundamental issue of trust between the European Union negotiators, the United Kingdom and ourselves,"
"When you enter into an agreement, solemnly engaged in hard-working negotiations and so on, you sign off, you go through your own parliament, and your own parliament approves this. Then you decide to undermine that international agreement.
"That has implications for the conduct of negotiations into the future."
Sinn Fein leader Mary Lou McDonald said the UK had "breached an international commitment and they need to get back in line". "I hear commentary coming from London from some who are looking to break international law and at the same time say that they're concerned to protect peace on the island of Ireland. To me, that's absolutely absurd. It's also dangerous," she added.