The Taoiseach says he knew some months ago that Michael Collins TD was in talks with the Revenue Commissioners about his financial affairs.
However Mr Ahern said the details of those discussions were not known to the Fianna Fáil Parliamentary Party.
The Taoiseach says Michael Collins will get every opportunity to explain his circumstances to the Public Offices Commission and to the Fianna Fáil ethics committee.
Labour leader Pat Rabbitte said Mr Ahern’s admission that he knew Mr Collins had tax “issues” was an extraordinary development.
He said: “The Taoiseach should now state clearly when exactly he first heard that Deputy Collins has issues.
“Did he call in Deputy Collins and ask him to outline the exact nature of the issues he had with the Revenue Commissioners?”