The Supreme Court has reserved its judgment in the action being taken by former Rehab Group CEO Angela Kerins against the Dáil's Public Accounts Committee.
Chief Justice Mr Justice Frank Clarke said the one thing agreed in the case is that it is "important and difficult."
Ms Kerins is appealing the High Court's dismissal of her action.
She claims two committee hearings in 2014, into money paid to the Rehab Group, amounted to a witch hunt against her.
Ms Kerins wants to claim damages for personal injury, loss of reputation and loss of career and she wants references to her and her employment with the group to be deleted from the committee's record.
She also wants declarations that what happened to her was unlawful.
The High Court found the courts could not intervene at all in relation to Dáil committee proceedings.
In their closing submissions, Ms Kerins' lawyers told the Supreme Court that the Constitution gives no immunity to parliamentary committees who unjustly attack the personal rights of a citizen.
Senior Counsel John Rogers said there was a limit to what an Oireachtas committee could do, and the Public Accounts Committee exceeded that limit by conducting an investigation into the internal business of Rehab and the private matters of Ms Kerins.
Mr Rogers said the most fundamental thing in the Constitution was the protection of the personal rights of the citizen through the courts.
He said the Oireachtas had failed to ensure protection for citizens in Ms Kerins' circumstances and the court was entitled to intervene where that was not provided.
Organs of the Oireachtas could not entirely ignore their remit for the purpose of having a go at someone, he said.
Mr Rogers argued that the Constitution must be read as a whole, there was no reference to Dáil committees in Article 15.13 protecting the speech of Oireachtas members, and it did not apply to committees at all.
Earlier, lawyers for the State agreed that people may not turn up at Oireachtas committees as a result of Ms Kerins' experience.
But Senior Counsel Maurice Collins said that, if the work of committees was diminished as a result, that was their own fault.
He said that outcome was more palatable than the consequences of Ms Kerins winning her appeal.
Mr Collins said the court was being asked to permit the sacrifice of the principle of the freedom of parliamentary speech, for Ms Kerins' personal rights.
He urged the court to decide the case "at the level of principle" unaffected by individual sympathy, even if the court had a strong impulse to provide a remedy for Ms Kerins.
Mr Collins said that, because of Article 15 of the Constitution, a citizen had no legal remedy concerning what was said about them in the Oireachtas by members and it was wrong to urge the court to find a way around that.
The Supreme Court will deal with the committee's appeal against the High Court's decision directing it to pay two thirds of Ms Kerins' costs after it gives its judgment.