Denis O'Brien will take his fight to limit Dáil privilege to the Supreme Court today.
The businessman says TDs shouldn't have discussed his finances in Leinster House.
Court Correspondent Frank Greaney reports:
In the summer of 2015 Catherine Murphy and Pearse Doherty spoke in Leinster House about Denis O'Brien's dealings with IBRC.
Mr O'Brien claims their comments unfairly revealed court protected details about his dealings with the state-owned bank.
Those comments were protected under Dail privilege -a rule which allows politicians to discuss import matters with other elected representatives.
Last year Denis O'Brien challenged that right the High Court and lost.
Ms. Justice Una Ní Raifeartaigh said to intervene would have a chilling effect on parliamentary speech.
Today that ruling is being appealed to the Supreme Court - the highest court in the country.