Renua leader and former Fine Gael Minister Lucinda Creighton said the Government just wanted the affair to go away and had set in train a situation that amounted to “naked political opportunism.”
Fianna Fáil also criticised the terms of reference for the proposed probe, saying the role of the Finance Department also needed to be looked at.
However, Minister of State at the Finance Department Simon Harris hit back, saying the opposition was delaying the outcome of the inquiry by saying it looked at more things.
Finance Minister Michael Noonan is to meet opposition counterparts on Monday to discuss the terms of reference ahead of a debate on the scope of the probe to be held in the Dáil on Tuesday.
The fact the Government has only allowed four hours for the debate has angered opposition TDs. Ms Creighton demanded that all IBRC deals that resulted in a loss of at least €1m be looked at rather than the €10m loss cut -off point at present.
The investigation will also look at writedowns, interest rates and whether any customers received preferential treatment from the institution formed out of Anglo Irish Bank and Irish Nationwide Building Society.
Fianna Fáil leader Micheál Martin said any possible lapses in corporate governance at the bank, and any deals not finalised when IBRC was liquidated in 2013, also need to be looked into.
Mr Martin said it was crucial that the investigation produce an interim report in case it drags on past the general election which must be held within 10 months.
Sinn Féin’s Gerry Adams also called for the commission to finish its inquiries by October, rather than the end of the year as envisaged by the Government.
Independent TD Catherine Murphy, whose probing of the issue revealed that IBRC had approved a deal to sell Siteserv to a firm controlled by billionaire businessman Denis O’Brien despite strong reservations from senior civil servants, said she would consider the terms of reference in the coming days.
“The one thing that I said I wanted was a credible, independent inquiry. I accept that when you’re looking at something in a different historical space you can use a different set of measures, and I said I would accept the findings if it was credible and I will,” Ms Murphy told RTÉ.
The TD said many serious questions were unanswered in the IBRC saga.
Ms Murphy expressed concern that “misplaced” documents which suddenly emerged in the Finance Department this week showed the taxpayer had lost €119m on the Siteserv deal, €9m more than previously stated.
Former IBRC chairman Alan Dukes said the former head of asset management at the bank Richard Woodhouse, played no part in the decisionmaking process around the sale of Siteserv.
The documents discovered by the Finance Department revealed Mr Woodhouse did attend meetings where the Siteserv deal was discussed.