TAOISEACH Micheal Martin is "not optimistic" a Brexit deal can be achieved following the British Government's move to override parts of the Withdrawal Agreement.
The Taoiseach spoke with British Prime Minister Boris Johnson over the phone yesterday evening about the serious implications breaching international law on the Northern Ireland protocol would have.
On Tuesday, Northern Ireland Secretary Brandon Lewis said legislation to change the Withdrawal Agreement goes against international law in a "very specific and limited way".
Speaking this morning, Mr Martin said he told Mr 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 center stage. That it was bad for Northern Ireland politics and would be divisive," Mr Martin told RTÉ 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 has raised a fundamental issue of trust between the European Union negotiators and United Kingdom and ourselves,"
"That when we 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, and then you decide to undermine that international agreement, that that has implications for the conduct of negotiations into the future."
The Taoiseach said Mr Johnson expressed a "full understanding" of the concerns over the British government signalling its intention to break an international treaty and the Northern Ireland Protocol.
"He has a full understanding of where I'm coming from and our views and also, I think the difficulties that this has now created in terms of the conduct of the negotiations. Because obviously, and I've been in touch with the President of the European Commission von der Leyen - spoke twice yesterday - they are taking this very seriously," he said.
Mr Martin said his trust in Mr Johnson has "been eroded", but added the British prime minister made it "very clear" that the UK is " fully committed to meeting its obligations in relation to the protection of the single market and in relation to the fluidity of trade with North and South."
"The legislation runs counter to that. But nonetheless, these were the assertions that the United Kingdom Prime Minister was very clear with me last evening. Obviously, then the joint committee meeting today will have that tested in it's full by the European Union leadership."
Mr Martin had earlier been under pressure to "publicly call out" the British prime minister.
Speaking in the Dáil on Tuesday, Labour Party leader Alan Kelly told the Taoiseach: "You need to stand up and call this out for what it is. I don't trust Boris Johnson - I know you can't say that, but you more or less have to, in diplomatic language, because this is unprecedented."
Sinn Féin leader Mary Lou McDonald said that Mr Johnson, if he got away with walking away from the Northern Irish protocol, "will feel emboldened to walk away from the whole lot".
"Perfidious Albion is alive and well and living at No 10 Downing Street," she added.