Independent TD Shane Ross has said the Public Accounts Committee has the capacity and mandate to examine allegations of a cover-up of tax evasion by former senior politicians.
Mr Ross said the committee's job is to establish whether or not State agencies have carried out their investigations properly.
Allegations of tax evasion are contained in a dossier that was sent to members of the Public Accounts Committee in recent days under new whistleblower legislation.
Mr Ross said it was apparent that the whistleblower, a serving civil servant, was frustrated with previous investigations of his allegations.
Meanwhile, the family of a former senior judge mentioned in the dossier say he never had an offshore account.
In a statement, the Costello family confirmed that former Attorney General Declan Costello, now deceased, had an account in Guinness & Mahon bank in the 1970s, the bank that also held offshore accounts allegedly belonging to former senior politicians.
The family states that Mr Costello's account was opened to receive £15,000 from the sale of his father's house and was a resident account on which tax on interest was paid.
Mr Costello led the High Court inspectors that investigated Ansbacher Cayman Islands offshore accounts.
The family say he did not recall the existence of the account when invited to act as High Court inspector in 1999, nor did he remember in 2004 when contacted by the author of the dossier, who alleges Mr Costello had a conflict of interest when investigating the Ansbacher accounts.
A spokesman for Minister for Jobs Richard Bruton has said the whistleblower has received a reply.
"This is the first case which has emerged to our knowledge under the new whistleblowers' legislation, and as such the minister and others are constrained as to what he can say in relation to it.
"As a matter of course, all correspondence on a subject like this would be responded to, and forwarded by the minister's office to the relevant officials for attention and action. This happened in this case. "
Taoiseach Enda Kenny has said the details would be fully examined.
Public Accounts Committee member Mary Lou McDonald yesterday said the tax evasion allegations and allegations of a failure to investigate them by State agencies merit full investigation.
