A key witness has questioned the validity of an Oireachtas inquiry into a £36 million overrun on a CIE rail signalling project.
Mr Leslie Buckley, who is central to the events under investigation, is understood to have claimed that the inquiry procedures were "fundamentally flawed".
His challenge is seen as a sign that he will mount a robust defence at the hearings by a subcommittee of the Oireachtas Joint Committee on Public Enterprise and Transport, which begin on Monday.
The sub-committee wants to establish why the estimated cost of the rail system rose to about £50 million, despite projections that it would cost £14 million.
The system is incomplete and the overrun has been linked to the construction in 1997 of a telecoms system along the CIE railway for Esat Telecom. Mr Buckley was acting chief executive of Esat Telecom at that time and he had worked previously as a consultant to Iarnrod Eireann, CIE's rail company.
Relations between the inquiry and Mr Buckley are said to be "difficult".
The inquiry's chairman, Mr Sean Doherty TD, said in a statement six weeks ago that the telecom network, which is complete, was a "very significant asset" for Esat.
He questioned why that project went ahead before the CIE signalling system, which was crucial to rail safety.
Mr Buckley's legal team is understood to have told the inquiry that its directions were "invalid" because it was not clear what his rights to privilege or to recover his costs were. He could not proceed without the same privilege given to witnesses in the High Court.
Last night, however, an Oireachtas spokeswoman said all witnesses would be entitled to absolute privilege once directed to attend. All reasonable requests to recover costs would be considered.
Mr Buckley's spokesman denied suggestions that he was preparing to seek an injunction to block the inquiry.
He said: "This suggestion is categorically false and mischievous. Mr Buckley has co-operated and responded promptly to all correspondence from the Oireachtas committee."
The inquiry is expected to hear evidence from 100 people and its hearings will halt work by up to 20 other Oireachtas committees for the next three weeks due to a shortage of staff.
They have been asked not to sit because "all resources" were going towards the inquiry, an Oireachtas spokeswoman said.
