Ten Provisional IRA prisoners who were being detained in Castlerea Prison were transferred last night to Portlaoise Prison.
The move surprised the Prison Officers' Association, whose members had been involved in discussions with the prison management over staffing levels and the relaxed regime for political prisoners at Castlerea.
A prison guard was detained by the IRA prisoners last Sunday and searches of the prisoners' bungalow accommodation in the prison grounds early yesterday uncovered tools, alcohol, a passport and £1,000 in cash.
A union source said: "This could have huge ramifications, because their treatment is a part of the Good Friday agreement. We're genuinely surprised, but it seems circumstances have overtaken events."
A statement from the Prison Service announced the transfer to Portlaoise at 6.30 p.m. "This decision was taken following events in the prison over the past 48 hours. It was decided in the circumstances that the transfer should take place now", the statement said.
"It was also decided that the prisoners should remain in Portlaoise pending completion of the ongoing investigation of recent events at Castlerea and pending full consideration by the authorities of the findings of that investigation."
None of the 10 prisoners - who include the four men jailed for their role in the murder of Det Garda Jerry McCabe - are entitled to early release under the terms of the Belfast Agreement. However, they were allowed prison concessions, which staff claim were abused.
Last Sunday a prison officer delivered a message to the lodgings of the prisoners, who were being housed in minimum-security bungalows in the grounds of the prison. The officer was detained by the prisoners for about 10 minutes before being released.
Sinn Fein last night expressed concern that the items recovered in the search of the prisoners' bungalows were being portrayed in a negative light.
In a statement, the party said that the passport which had been found had been returned to one of the prisoners by a detective six weeks previously. "Furthermore, the £1,000 that has been referred to is money which belongs to all 10 republican prisoners and is used as a float for telephone calls and food.
"It is clear that those with an agenda against the remaining republican prisoners in Castlerea have been attempting to manipulate the media in order to present these matters in a very sinister light."
Mr Sean Alyward, director-general of the Prison Service, said yesterday evening that the items found in the prison search placed a question mark over the less stringent regime which had been applied to the political prisoners.
The 10 IRA prisoners spent last Sunday commemorating the 1916 Rising. Before detaining the guard in the evening they had paraded in military-style garb and consumed alcohol.
Mr Jim Higgins, the Fine Gael spokesman on justice, said yesterday that the Minister for Justice, Mr O'Donoghue, was "politically responsible for the breakdown of prison order".
Mr Higgins said he was reluctant to say that the entire prisoners' deal under the Belfast Agreement should be nullified, until such time as the agreement was deemed "unsalvageable", but the special concessions should be re-examined.
He added: "The concessions were given on the basis of the Good Friday agreement and part of that agreement has not been honoured by the IRA."
A prison source said staff at Castlerea had been concerned for some time at the relaxed regime for political prisoners.