Finance Minister Michael Noonan has told the North's finance committee that NAMA is accountable to the Public Accounts Committee only, and no-one else.
The committee wants to quiz NAMA officials about corruption allegations surrounding the purchase of the agency's Northern Ireland portfolio.
Minister Noonan had been accused of snubbing the inquiry, after he failed to respond to a series of letters from them.
However, the group received a response from the Department of Finance yesterday.
Chair of the North's finance committee Sinn Féin MLA Daithi McKay said NAMA's failure to answer their questions reflects poorly on the agency.
"We are trying to get a number of witnesses before us - a lot of the witnesses are evasive, and that reflects badly on all of them, that they're not willing to speak to ourselves," he said.
"The public, north and south, are concerned about some of the allegations that have been made - and, of course, the fact that taxpayers' money is involved."
Separately, Fianna Fáil's Michael McGrath has formally written to the IBRC Commission of Investigation's chairman, Justice Brian Cregan, with evidence revealed at the Banking inquiry last week.
Last Thursday, IBRC's former chief executive Mike Aynsley told the inquiry that the Department of Finance had tried to interfere in the sale of major assets by the bank.
Deputy McGrath says the Banking Inquiry has been given legal advice saying it is not the correct body to investigate the claims - so they are being referred to the Commission of Investigation instead.