Real IRA leader Michael McKevitt is applying for his immediate release in the High Court.
The 59-year-old from Beech Park, Blackrock, Co Louth, is relying on recent legal rulings that his lawyers say entitle him to enhanced remission of up to one-third off his 20 year sentence.
Michael McKevitt was jailed for 20 years in 2003 for directing terrorism and for membership of the Real IRA.
He is due for release from Portlaoise prison in April 2016 but he claims he is entitled to benefit from an enhanced remission scheme that would see him get out of jail immediately.
He argues the Justice Minister is obliged to cut up to a third off his jail time because he has complied with a rule to be of good conduct and engage in authorised, structured activities aimed at decreasing the likelihood of reoffending.