Independent TD Michael Lowry has begun an appeal over the Moriarty Tribunal's decision to award him just one third of his legal costs.
Mr Lowry is appealing against the High Court's refusal to order the tribunal to pay the full costs of his participation in the inquiry.
The tribunal found he failed to fully co-operate with it.
His Senior Counsel Niamh Hyland told the three-judge Appeal Court that the tribunal had been extraordinarily long and Mr Lowry had been obliged to interact constantly with it.
She said depriving Mr Lowry of two thirds of his costs, means he had been subjected to a penalty because the costs, estimated at millions of euro, were so very large.
She said the tribunal's decision had had an adverse effect on Mr Lowry's family life, privacy and health.
She said one of the reasons put forward by the tribunal for depriving him of the costs was that he had contributed to the extraordinary length of the tribunal.
She said this could not be laid at Mr Lowry's door.
Ms Hyland pointed out that the tribunal had also investigated former taoiseach, the late Charles Haughey and he had received all of his costs. She said this was a very important part of Mr Lowry's case.
She said the tribunal was supposed to act in a way that was consistent, rational and constitutional.
The hearing will continue tomorrow and judgment is expected to be reserved to a later date.
