Businessman Denis O'Brien has begun his appeal against the High Court's dismissal of his action over statements made in the Dáil about his banking affairs.
Mr O'Brien is appealing against the court's decision that it had no power to rule on issues raised by him about how the Dáil's Committee on Procedure and Privileges dealt with the statements and with his complaints.
He is also appealing against an order directing him to pay the costs of his failed High Court case.
Mr O'Brien was granted an injunction in April 2015 against RTÉ in relation to a proposed broadcast about his banking affairs.
He says Social Democrats TD Catherine Murphy and Sinn Féin TD Pearse Doherty then revealed information on the floor of the Dáil which rendered the injunction almost pointless.
The Dáil Committee on Procedure and Privileges found the TDs had not breached the relevant rules.
Mr O'Brien is seeking a declaration that the committee's finding was based on an error in interpreting the relevant Dáil standing order.
He also wants a declaration that there was no evidence for the committee to make a finding that Ms Murphy acted in good faith.
The High Court ruled against him, saying the constitution did not allow the courts to adjudicate on statements made in the Dáil or on how the Dáil committee dealt with the matter.
Mr O'Brien is appealing the court's finding relating to the committee.
He says the High Court got it wrong and its ruling means members of the Oireachtas can subvert court orders in the parliamentary process and flout their own rules, with no remedy for him or others like him.
Senior Counsel Michael Cush told the seven-judge Supreme Court that Mr O'Brien was a citizen who was not a member of either house of the Oireachtas.
He had the right to the confidentiality of his private banking affairs.
Mr Cush said Mr O'Brien had the right to have his legal action against RTÉ over his banking affairs determined by the court.
He said Ms Murphy and Mr Doherty had encroached on those rights.
He added that Mr O'Brien had the right to have his complaint to the Committee on Procedure and Privileges properly determined in accordance with a correct interpretation of the standing orders.
Mr Cush said Mr O'Brien's constitutional rights were deliberately damaged by the deputies' utterances and making a complaint to this committee was Mr O'Brien's only remedy.
He wanted to establish that what was done was wrong and to minimise the prospects of it happening again in future to him or to others.
He said Mr O'Brien's interests were directly and centrally affected - he was not just a disinterested spectator.
Mr Cush said that out of 178 standing orders regulating the conduct of the Dáil, only three dealt directly with the interests of non members.
He said deputies Murphy and Doherty had given no notice of what they were going to say.
He added the Committee was arguing that no notice was required in the circumstances.
Mr Cush said it had emerged in the High Court proceedings that the Committee had not sought a response from the deputies to Mr O'Brien's complaint and a response had not been proffered.
This was the basis for Mr O'Brien's assertion that there was no evidence to support the Committee's finding that Catherine Murphy had acted in good faith.
Mr O'Brien is also appealing the High Court's finding that the case was not novel enough to depart from the normal rule that the losing party pays the costs.
Lawyers for the Dáil's Commitee on Procedures and Privileges said the two TDs had not breached the High Court injunction granted to Mr O'Brien against RTÉ, as it had been made clear to the High Court that it was never intended to apply to deputies on the floor of the house.
Senior Counsel Michael Collins said the Committee was the way the Dáil had chosen to make TDs amenable for what they say in the house.
It was clearly not conceivable, he said, that the court could interfere in that process.
Article 15 of the Constitution contained provisions that deputies could not be amenable to anyone other than the house itself for what they say.
He said the committee had not infringed on Mr O'Brien's constitutional rights in any shape or form.
Earlier, lawyers for Mr O'Brien told the Supreme Court that the freedom of speech protected by Article 15 of the constitution was freedom of speech that respected the separation of powers between the Oireachtas and the judiciary.
The case will continue tomorrow.