There are strong denials that overcrowding was to blame for a riot at Mountjoy jail which saw three prison officers injured.
The garda riot squad had to be called in after a group of up to 70 inmates, armed with snooker cues and table legs, barricaded themselves into an outdoor area.
The Prison Officers Association said the atmosphere in Mountjoy is a "like a tinderbox waiting to ignite again". The IPOA also maintains the tensions are fuelled by an ongoing overcrowding crisis.
However Brian Purcell, Head of the Irish Prisons Service, said the real reason behind the riot was the continued clampdown on contraband.
"Overcrowding within the system can be problematic, but…the cause of the incident last night was not over-crowding," he said.
"That was down to a prisoner reaction to an on-going campaign to crack down on illicit items being brought into the prison - drugs, mobile phones and other contraband."