Two men, including Gerry "The Monk" Hutch, claim they should not be tried before the non-jury Special Criminal Court (SCC) on charges of murder arising out of the Regency Hotel attack in 2016.
Hutch (58), who was extradited from Spain, and former Sinn Féin councillor Jonathan Dowdall (44), of Navan Road, Dublin, are both charged with the murder of David Byrne (33) at the hotel in Whitehall, Dublin on February 5th, 2016.
They are both seeking declarations from the High Court that their trials before the SCC will be unlawful and in breach of their fundamental rights because the SCC is operating as a permanent court when it was only set up on a temporary basis nearly 50 years ago.
Their judicial review proceedings are against the Minister for Justice, Dail Eireann, Ireland and the Attorney General, while Seanad Eireann is also a respondent in the Hutch case.
Both men seek various declarations, including that a trial before the SCC is unlawful, outside the powers of the 1939 Offences Against the State Act, and violates their constitutional and European Convention rights.
They also claim the failure by the State to enact anything other than temporary measures in respect of procedures for the trial of persons before the SCC also breaches their rights.
They say they should not be tried under what amounts to temporary legislation introduced in 1972 during the Troubles in response to an emergency situation at the time, but has since been extended to deal with serious organised crime.
The respondents deny their claims and say, among other things, there is a failure by the men to adequately, or at all, particularise the legal basis for the reliefs they seek.
Michael O'Higgins SC, for Mr Dowdall, argued that the court would have to decide whether a proclamation in 1972, setting up the SCC for the third time in the State's history on a temporary basis, has now morphed into a permanent situation.
It was his side's argument that this was outside the powers of the Offences Against the State Act and if the State wanted to make it permanent it should introduce legislation permitting it to do so.
Counsel said the substantive argument in this case related to statutory interpretation of the law governing the setting up of the SCC.
The hearing continues before Mr Justice Anthony Barr.