Mr Mark FitzGerald, son of former Taoiseach Dr Garret FitzGerald and one-time a Fine Gael trustee, is due to appear before the Moriarty tribunal today.
The inquiry in Dublin Castle is beginning a new module in which it will look at payments to Fine Gael during the mid-1990s when it formed part of the rainbow coalition.
It may also hear evidence from the Fine Gael leader, Mr Enda Kenny.
Evidence is expected from Mr FitzGerald concerning a conversation between him and the then Fine Gael minister Mr Michael Lowry, in 1995, concerning the rent paid by the State to Mr Ben Dunne, a major contributor to the party.
Statements of intended evidence made by Mr FitzGerald to the tribunal last year led to tensions within the party. His statement may lead to a number of party figures having to appear to give evidence.
Mr FitzGerald was a party trustee for many years but left the board of trustees in June last year. Mr Lowry was chairman of the board of trustees in the mid-1990s.
Mr FitzGerald, of estate agents Sherry FitzGerald, told the tribunal in a statement of intended evidence last year, that Mr Lowry tried to help Mr Dunne to get a 100 per cent rent increase for a 90,000 sq ft office block in Dublin being rented by Telecom Éireann.
The increase would have seen the rent go from £450,00 per annum to £900,000 per annum. In the event, the rent for the office block was increased to £540,000 per annum.
Mr Lowry, in a statement of intended evidence, has denied the allegation. He has said he agrees the two men discussed the issue but he "rejects absolutely" any suggestion that he tried to influence the arbitration which was then under way into the issue of the rent which would be paid by Telecom Éireann.
The arbitrator involved worked for Sherry FitzGerald.
Details of the statements of intended evidence were read out by tribunal counsel Mr John Coughlan SC in December 2002. At the time Mr Dunne had not yet filed a statement of intended evidence.
Mr Coughlan said the matter warranted serious investigation and inquiry and was relevant to matters heard by the McCracken tribunal in 1997 and the Moriarty tribunal two years ago. Mr FitzGerald made his statement in November 2002.
The Moriarty tribunal has already looked into a $50,000 contribution made by Esat Digifone/Telenor to Fine Gael in late 1995-early 1996.
It is now expected to look at a number of other smaller contributions made by Mr Denis O'Brien or his companies to Fine Gael.
The tribunal has been told that Mr O'Brien engaged a Fine Gael activist, Mr Dan Egan, at the time of the mobile phone licence competition.
Mr Egan is to say Mr O'Brien wished to raise his general profile, including his profile with Fine Gael and that he, Mr Egan, advised him that he should attend Fine Gael fund-raising events, at which he could meet ministers in an informal setting.
In an opening statement last year, tribunal counsel Mr John Coughlan said that among the meetings arranged by Mr Egan was one between Mr Enda Kenny and Mr O'Brien.
At the time, Mr Kenny was minister for tourism and trade. An entry in Mr O'Brien's diary said the meeting occurred in Government Buildings in May 1995. The same day Mr O'Brien met Mr Richard Bruton.
