The Public Accounts Committee has been told that Angela Kerins will threaten legal action if more details of her salary and conditions are revealed.
Rehab officials have told the committee that the group received legal letters from Ms Kerins last night.
The P-A-C was told this morning that Frank Flannery has also refused to reveal any of his pay or pension entitlements.
The chairman of Rehab's remuneration committee Declan Doyle says the group's hands are now tied.
Meanwhile it's emerged that Frank Flannery received over 400,000 euro in consultancy fees from Rehab after stepping down.
The committee has been told that the fees were at a level which could have been unilaterally approved by Ms Kerins.
The committee's also disclosed the salaries of seven other senior executives at the Rehab Group.
The seven directors, each of whom are responsible for separate parts of Rehab's operations, earn a combined salary of close to one million euro a year.
