The Sinn Fein president, Mr Gerry Adams, will join protesters outside the High Court today when attempts will be made to legally block the extradition to the North of the former IRA prisoner Angelo Fusco.
Fusco (43) from west Belfast, was arrested in Co Kerry last Monday after being on the run for more than two years.
He was to have been handed over to the RUC on Tuesday for the 1980 murder of SAS Capt Herbert Westmacott.
However, after an application by lawyers acting for Fusco, a convoy of Garda cars taking him to the Border was halted on the orders of the High Court.
Mr Justice Finnegan directed that Fusco should be brought before him today.
Fusco's legal team will argue that extradition warrants issued against him, and later upheld by the Supreme Court, should no longer apply because of "profound" changes generated by the Belfast Agreement.
Fusco was convicted in his absence in Belfast in June 1981 of murdering Capt Westmacott.
He and seven other accused men had shot their way out of the court building before being sentenced to life imprisonment.
Gardai arrested him the following year and he served almost 10 years in Portlaoise Prison for escaping from Belfast.
On his release in 1992, the extradition warrants were served.
After a six-year battle against extradition, Fusco absconded when the Supreme Court vindicated the warrants in 1998 and directed that he be returned to the North to finish a life sentence.
If Fusco is returned to the British jurisdiction, he could get temporary parole from the Maze Prison, which is now almost empty because of the early prisoner release programme under the Belfast Agreement.
He could be freed within weeks.
If returned to custody in the Republic, he is likely to be freed on bail.
Mr Adams said last night he would attend the hearing and join the public protest due to be staged outside the High Court opposing Fusco's extradition.
Mr Martin Ferris, a member of the Sinn Fein team which negotiated the Belfast Agreement, said: "This is an issue of concern to everyone across the political spectrum perturbed by the indecent haste by certain agencies to extradite Angelo Fusco in clear breach of the Good Friday agreement."