Former minister for communications Michael Lowry is being sued by his accountancy firm over an unpaid bill of more than €1 million.
Foxrock-based BBT accountants lodged the case in the High Court in recent weeks.
Mr Lowry has confirmed to RTÉ News that the accountancy firm is suing him.
He said the lawsuit related to unpaid fees outstanding since the conclusion of the Moriarty Tribunal, at which Mr Lowry was a witness since it began in 1997 to its final report in 2011.
BBT accountants lodged a High Court action against Mr Lowry two years ago, back in 2011, before withdrawing the case shortly afterwards.
Neither BBT nor Mr Lowry commented on that legal action at the time.
BBT did not reply when contacted by RTÉ News.
The fees are understood to be in the region of €1.4m.
The tribunal investigated links between Mr Lowry and Denis O'Brien over the awarding of the 1995 mobile phone licence to Esat.
The report stated it was "beyond doubt" that Mr Lowry imparted substantive information to Mr O'Brien which was "of significant value and assistance to him in securing the licence".
Both Mr Lowry and BBT accountants have made separate applications to the tribunal for fee payments.
However, the tribunal has not yet issued a cost order in relation to Mr Lowry's fees for work done by BBT.