Businessman Denis O'Brien wrote a personal letter last month to the chairman of the Moriarty tribunal, Mr Justice Michael Moriarty, claiming the tribunal was "totally biased".
At a sitting of the tribunal today, the chairman said Mr O'Brien had written that the tribunal's "activities really reach a new low in Irish judicial history".
Mr Justice Moriarty also complained about the prevalence of public relations and spin that was taking place outside the tribunal and would not be welcomed by the courts.
However, he said he would base his report on the evidence and what "stacked up". He particularly mentioned Mr O'Brien's public relations officer, James Morrisey, who was at the tribunal.
Mr Justice Moriarty said he had been a judge for 23 years and he was "bemused" at some of the remarks that were being made outside the tribunal that it was "seeking to cobble together a report" that would "unjustly condemn" people for whatever reason.
He said this was an "unthinkable suggestion" for a judge appointed to a tribunal by both houses of the Oireachtas.
Evidence is being heard from Attorney General official Denis McFadden, who says he has no doubt that Richard Nesbitt SC gave advice in 1996 that the State's second mobile phone licence could be issued to Mr O'Brien's Esat Digiphone.