The Taoiseach Micheál Martin has critised Labour leader Alan Kelly over comments made in the Dáil on Tuesday.
Mr Martin says Deputy Kelly came over to him to clarify new rules around households having to isolate for five days with a COVID case.
At which point, the Taoiseach claims, Mr Kelly falsely reported that teachers were exempt from the change.
Speaking in the Dáil on Wednesday, Mr Martin says he will not forget what happened.
"I've been in the House longer than you, and you learn something every day.
"And I learned something about you yesterday that I will not forget, and that will govern our relationship from here onwards.
"I've never seen the likes of it before".
Mr Martin says the Labour leader wanted to know if the Government would priortise certain sectors - like teachers - for boosters.
"You asked the Taoiseach nothing about household contacts... nothing at all about it. I just put that on the record.
"And suddenly you come over here for 30 or 40 second engagement, you scamper up - you tell your education correspondent who tweets something and it's reported as fact.
Mr Kelly then replied from across the Dáil chamber: "If you want to call me a liar, call me a liar".
To this, the Taoiseach said: "I never said what you construed that I said.
"I rang you afterwards to make it very clear to you how I regard the interchange.
"You can't do things like that".
In a statement on Tuesday evening, Deputy Kelly doubled down on his claims.
He said he "engaged directly" with the Taoiseach on behalf of teachers and SNAs after Dáil questions.
"I don't believe teachers should be discriminated against or treated differently so I raised concerns about the impact the proposed five-day rule for household contacts of confirmed cases would have on schools", he said.
"The Taoiseach clearly told me teachers were exempt from this rule. I did not misconstruct what he said – far from it.
"It's obvious that as a result of my colleague and our education spokesperson Aodhán Ó Ríordáin bringing this to public attention, the Government reversed position rapidly.
"It says so much about the incoherence of this Government that policy changes by the hour, and at some stages they don't know what U-turn they are even reversing."