The Dáil Committee on Procedure and Privileges has declined to give the Public Accounts Committee permission to compel former Rehab chief executives Angela Kerins and Frank Flannery to appear before it.
The Committee on Procedure and Privileges said it had made its decision based on legal advice from senior counsel Caroline Costello.
The advice stated that the PAC is only empowered to proceed with the examination of an account audited or report prepared by the Comptroller and Auditor General.
It noted that Rehab is not audited by the C&AG and accordingly no report exists.
The PAC does not have the legal authority to examine the use of public monies by the Rehab group.
Both Mr Flannery and Ms Kerins refused to appear before the committee earlier in April.
However, the CPP has agreed to give the PAC the power to compel three witnesses in relation to the operation of the National Health and Local Authority Levy Fund.
The controversial training fund had millions of State funding.
The PAC was also given the power to compel a report into the operation of the fund.