The Taoiseach has told the British Prime Minister Boris Johnson his concerns about Brexit "in forthright terms" this evening.
Micheál Martin set out his apprehension about the latest developments in London during a phone call with his British counterpart.
Mr Martin cited the breach of an international treaty, the absence of bilateral engagement and the serious implications for Northern Ireland as among his concerns.
The Taoiseach also stressed that the UK government "should re-engage with EU negotiators urgently".
It comes after the controversial Internal Market Bill was published by the British government today.
The Bill aims to override parts of the Brexit deal relating to Northern Ireland, which would happen in an event no trade deal is reached between the UK and EU.
The British government has admitted that the Bill breaks international law, with the draft legislation saying: "Certain provisions to have effect notwithstanding inconsistency or incompatibility with international or other domestic law."
The Bill has been met with criticism both at home and abroad, with the Foreign Affairs Minister Simon Coveney accusing the UK government of taking an "aggressive and illegal" course of action on Brexit.
He added that Northern Ireland is too fragile to become a pawn in the Brexit negotiations.
The Sinn Féin leader Mary Lou McDonald told The Hard Shoulder it's "astonishing" that the British government is being so brazen.
She said Boris Johnson and the Tories are "very, very wrong" if they think they can get it all their own way.
Earlier, the Tánaiste Leo Varadkar said the latest move by the UK government was "constitutionally reckless" and urged two of the country's highest-ranking officials to "consider their oaths".
