The Government is facing a motion of no confidence later
Fianna Fáil's justice spokesman Jim O'Callaghan says he is '100% certain' he told Tánaiste Frances Fitzgerald last Wednesday about false Tusla allegations against garda whistleblower Maurice McCabe.
Ms Fitzgerald has insisted she only learned about the Tusla allegations in media reports on Thursday.
In a statement Sunday, Ms Fitzgerald said: "Deputy O'Callaghan spoke to me about the terms of reference the day before the Dáil debate (Wednesday).
"He suggested the terms of reference should be broadened to bring absolute clarity that the allegation of criminal misconduct against Sergeant McCabe and the alleged smear campaign would be investigated.
"Deputy O'Callaghan said to me that PrimeTime would have a programme the following evening related the establishment of the Commission.
"At no point did he mention Tusla or any of the details that emerged in the programme," she added.
But Mr O'Callaghan says his party leader Micheál Martin phoned him last Wednesday at 7.30pm, where he was told he had received a phone call from Mr McCabe.
Mr McCabe had told Mr Martin a 'PrimeTime' programme on a Tusla file containing a false allegation against him was to be broadcast on the Thursday night.
"Micheál Martin was asking me whether the terms of reference - that had been published about one and a half hours earlier - was broad enough to cover that.
"My view was that it wasn't broad enough...We decided that I would go and talk to the Tánaiste about it.
"We believed the terms of reference needed to be extended because of this forthcoming allegation that was going to be broadcast on RTÉ the following night."
Mr O'Callaghan told Newstalk Breakfast: "I left that meeting with an instruction from my party leader (Micheál Martin) to contact the Tánaiste, I phoned her, she answered her phone.
"I asked her was she in the vicinity of Leinster House, she said she was - she was a Fine Gael Parliamentary Party meeting.
"I said to her I needed to speak to her face-to-face, which was unusual in itself. She agreed - she came downstairs and we met in the members' section of Leinster House.
"I told her that there was an issue about a Tusla file that was going to be broadcast on PrimeTime on the Thursday evening - I told her that in my opinion the terms of reference were not sufficiently broad.
"We then had a discussion for about seven or eight minutes about paragraph B of the terms of reference.
"I felt we were doing the Government and Tánaiste a favour by dealing with it in this way - we were forewarning them about the fact that there was this programme coming up.
"I said the Government could end up with egg on its face if there's a terms of reference agreed and then on the Thursday night there's a programme that comes out and it would particularly bad.
Mr O'Callaghan says he is "100% certain" he told the Tánasite about the Tusla file and its details.
It comes as Sinn Féin will publish a motion of no confidence in the Government later.
The party is seeking support from Fianna Fáil and from opposition TDs for the vote, which will be held in the Dáil this week.
Sinn Féin Deputy Leader Mary Lou McDonald says people 'the length and breadth of Ireland' are outraged over the Government's handling of allegations against Garda Sergeant McCabe.