Lawyers acting for the sister of one of loyalist Michael Stone's murder victims are to challenge the decision to release him on parole.
An emergency judicial review has been issued which seeks to challenge the legality of the decision by the Parole Commissioners to release Stone from Maghaberry Prison on Tuesday.
The case will be heard in Belfast's High Court on Thursday morning.
It will also challenge the decision of the commissioners not to provide reasons for Stone's release, their refusal to provide documents or information about the proceedings or allow the relatives of his victims to participate, a solicitor acting for them has said.
Mr Paul Farrell, who is acting for Deborah McGuinness, the sister of Milltown Cemetery attack victim Thomas McErlean, said on Wednesday evening: "This case is of huge importance not only to the victims of Michael Stone and their families but also it will have huge ramifications with regard to the future of Parole Hearings in Northern Ireland."
The release of Stone has been met with condemnation by victims' families after legal battles sought to keep him in prison until 2024.
The issue under consideration was whether he would stay in jail until then, or whether his minimum tariff expired in 2018, including the six years he was freed under licence.
Stone was serving a 30-year jail term but launched an appeal against efforts to keep him in prison.
The court concluded that the period that the prisoner spent lawfully on licence ought to be included in the relevant part of his sentence.
In 1988, Stone killed three people in a gun and grenade attack at Milltown Cemetery in Belfast and was freed early from prison in 2000 under the terms of the Good Friday Agreement.
He was sent back six years later after attempting to attack Sinn Fein leaders Gerry Adams and Martin McGuinness at Stormont.
The former UDA man was also the gunman in another three murders.
Milkman Patrick Brady was murdered in south Belfast in November 1984, 12 months before joiner Kevin McPolin was shot in the head in Lisburn, Co Antrim.
In May 1987 Dermott Hackett, a bread server, was found dead in his van between Drumquin and Omagh. He had been shot up to 16 times with a submachine gun.