The legal action arose out of statements made in the Dáil
The High Court has reserved judgement on whether a Harvard professor of constitutional law should give evidence in a case taken by Denis O'Brien.
The businessman claims statements made by certain TDs in the Dáil about his banking affairs were not protected by absolute privilege.
This legal action arose out of statements about Mr O'Brien's banking affairs with IBRC, which were made in the Dáil by Social Democrats TD Catherine Murphy and Sinn Féin's Pearse Doherty.
Parliamentary speech in Ireland is covered by absolute privilege but Mr O'Brien claims there is no such protection for the comments made by the two deputies.
His side wants to call Professor Laurence Tribe: an expert in constitutional law at Harvard Law School.
But Maurice Collins, who is acting for the State and the Attorney-General, is objecting because he says the issue of US law is not alive in this case.
Sara Moorhead, for the Dáil Committee on Procedure and Privileges, also objected. Said she was surprised with the extent of the reliance on Professor Tribe's report.
Mr Justice Peter Kelly will deliver his judgement at a later date.