The Dáil's Public Accounts Committee is to seek independent legal advice over its attempt to compel witnesses.
One member says there's an attempt to hinder the committee, after it was told it must provide more information on the request to force Angela Kerins and Frank Flannery to give evidence over funding and expenditure at Rehab.
"This is a refusal by any other name," said Deputy Shane Ross.
"The rest of the requirement for more detail is simply a challenge to us to put up more stuff which they will, in due course, refuse - on either legal or spurious grounds.
"I think it's probably an attempt to nobble it, and see that we don't seek or get compellability."
The Committee on Procedures and Privileges sent the letter this morning.