INCREASED custodial terms applied retrospectively to men caught in a surveillance operation targeting the Continuity IRA represents a "nadir of unfairness", the Court of Appeal heard.
Defence lawyers argued that newly introduced terror legislation which pushes back their clients' release dates is incompatible with the European Convention on Human Rights.
Six of the men imprisoned last year over the MI5 bugging operation focused on a house in Newry, Co Down are challenging their sentences.
Judgment was reserved following a two-day hearing into laws introduced by the British government.
Under the Counter Terrorism and Sentencing Act 2021, brought in after attacks at Fishmongers Hall and Streatham in London, offenders in Northern Ireland must now serve two thirds of their term behind bars.
Their cases also have to be referred to Parole Commissioners before any release.
The new Act has already impacted on Seamus Morgan (65) who is serving a three-year sentence for belonging to a proscribed organisation in connection with the secret recordings in 2014.
Morgan, of Barcroft Park in Newry, was told he would serve 18 months in custody and 18 months on licence.
Originally set for release in June this year, that date has now been put back to December at the earliest.
Barrister John Larkin QC claimed the new terms breach his client's right to face no retrospective penalty.
"What the govenment has done is create something of a nadir of unfairness," he submitted.
Contending that there is no justification for the increased punishment, Mr Larkin branded the situation "appalling".
Five of the other men jailed for offences connected to the MI5 operation are also seeking declarations that the Act is incompatible with their human rights.
They are: Patrick Joseph Blair (66) of Lissara Heights, Warrenpoint, Co Down; Joseph Matthew Lynch (80) from Beechgrove Avenue, Weston, Co Limerick; Liam Hannaway (51) of White Rise in Dunmurry, west Belfast; KevinmJohn Paul Heaney (48) of Blackstaff Mews, Belfast and Terence Marks (61) of Parkhead Crescent in Newry.
Mr Larkin, who also represented Marks, acknowledged the "horrifying attacks" in London which led to the new legislation.
But referring to his clients, he insisted: "These aren't dangerous people and they shouldn't be punished for the faults of others in a different jurisdiction.
"When one pleads guilty on advice one is entitled to be sentenced in accordance with the law as it then stands, and for that law not to be retrospectively changed."
Following closing arguments Lord Justice Treacy said: "The court wishes to reflect on the detailed submissions and will deliver judgment in due course."