Businessman Denis O'Brien is seeking to restrict the chairman of the Moriarty tribunal as to the type of conclusions he can make in his pending report.
The outcome of the challenge is likely to affect the reports of all tribunals, including the Mahon tribunal which is inquiring into the finances of Taoiseach Bertie Ahern.
Mr Justice Moriarty's second report will concentrate on payments to the former communications minister Michael Lowry.
It has inquired into possible payments by Mr O'Brien to Mr Lowry and the circumstances surrounding the awarding of the State's second mobile phone licence to Mr O'Brien's Esat Digifone, in 1996.
Mr O'Brien wants Mr Justice Moriarty to apply a standard of proof to his findings, rather than express "reasoned opinions" as he did in his report on the late Charles Haughey.
The matter is expected to be aired in a public sitting of the tribunal with legal submissions from a range of parties, including Mr O'Brien. Counsel for the public interest, instructed by the Attorney General, Paul Gallagher, may also make a submission.
If Mr O'Brien is not successful, it is likely he will appeal the tribunal's ruling to the courts, a development that could delay publication of the tribunal's report for some time.
In his report on payments to Mr Haughey, published last December, Mr Justice Moriarty said the findings represent "no more than what should be a reasoned and informed expression of opinion". He also said that court rules for the admission of evidence or the burden of proof would "inhibit . . . the functioning of the tribunal".
Mr O'Brien, in a submission by his lawyers, has argued that Mr Justice Moriarty was mistaken in this approach, which he says is a deviation from the practice of earlier tribunal reports.
He argues that Mr Justice Moriarty must make findings of fact, to a heightened civil standard of proof, basing the findings only on sworn evidence properly heard and not on hearsay and unproven documents.
Mr O'Brien "and others face the prospect of the tribunal reaching findings which are, in reality, not findings of fact but rather expressions of opinion", he has said.
"If a tribunal is going to declare publicly that a person is corrupt it should only do so based on solid findings of fact derived from sworn evidence. There is no such evidence against [Mr O'Brien]."
Mr O'Brien's submission continues: "As a person who has worked hard to build up successful businesses employing many thousands of people and as someone who has devoted considerable time to worthy causes, it would be wrong for the tribunal to rubbish this reputation based on anything other than findings of fact which have been properly proven to a very high level."
