The decision of a Colombian appeal court to sentence three Irishmen to 17 years in jail is outrageous, Sinn Fein's Gerry Adams has said.
Arrest warrants have been issued for the three men
Niall Connolly, Martin McCauley and James Monaghan were acquitted in April of training Marxist rebels in the country but this has been overturned.
Arrest warrants have been issued for the three republicans, who have remained on bail in Colombia.
The Sinn Fein President said it was a "grievous miscarriage of justice".
The three, who had been accused of being IRA members, were found guilty of travelling on false passports.
They were acquitted of the more serious offences by a lower court earlier this year, but the Colombian Attorney General has now successfully appealed against that decision.
Irish Foreign Minister Dermot Ahern said Dublin government officials would be in contact with Colombian authorities in the next few days.
"My initial reaction is surprise at the overturning of the verdict, given the complete exoneration in the lower court, and secondly, the severity of the sentence," he said.
Catriona Ruane of the Bring them Home campaign called on the Irish Government to intervene and would bring in international groups.
"This is a political decision and a blatant miscarriage of justice," said the Sinn Fein assembly member.
Welcoming the sentence, DUP assembly member Ian Paisley Jr said the "decision has far wider ramifications that what's happening in the judicial system in Colombia".
"Let's face it, Sinn Fein are psychologically still a war machine - their activists are across the world engaging in war activities, and I think that says an awful lot for the political process here," he said.
A judge had ordered the men to remain in the country pending an appeal by the prosecution against their not guilty verdict on training Farc guerillas.
The Colombian court system goes into recess on Friday, and the men's lawyers are expected to see them within the next day.
It is understood there is one final step in the legal process open to the men, an extraordinary appeal to the Supreme Court.
The earliest that any appeal can be lodged is mid-January.
McCauley, 41, is from Lurgan in County Armagh, Monaghan, 58, is from County Donegal and Connolly, 38, is from Dublin.
The three had been detained at Bogota's El Dorado airport in August 2001 as they were about to board a flight out of the country.
Their arrest led to speculation that Irish republicans had formed links with the Revolutionary Armed Forces of Colombia (Farc).
The main charge against them was that they had been teaching the rebels the techniques of urban terrorism.
The Irishmen strenuously denied this, saying they were in the area to monitor the fledgling peace process as well as being eco-tourists.