The High Court Taxing master has ruled that Liam Lawlor must pay legal fees of €500,000 for his participation so far at the Planning and Payments tribunal.
The bill presented to Mr Lawlor, of Lucan in West Dublin, was reduced by €50,000 following an appeal by the former Fianna Fail TD.
Taxing Master Charles Moran reduced the bill following a legal challenge from Mr Lawlor.
Moran granted Lawlor a 21-day stay on the ruling in the event of an appeal.
The former Dublin West TD was not in court for the ruling.