Balloting is expected to last two weeks, following the decision on Thursday to ballot for industrial action after a meeting between prison officers in Mountjoy and union representatives. Staff at the Dublin prison also passed a unanimous vote of no confidence in Brian Purcell, director of the Irish Prison Service.

Prison officers opted to ballot for strike action after the Irish Prison Service rejected their calls to declare a state of emergency in Mountjoy following a spate of violence, including the murder of a 21-year-old prisoner. Staff inside the prison have claimed that tension among prisoners is at breaking point and have voiced concerns over their safety unless additional staff are drafted in.

The deputy general secretary of the Prison Officers' Association (POA), Eugene Dennehy, says that officers are "hugely concerned" for their personal safety.

Dennehy claims that workshops and libraries in the prison have been closed down over recent months due to budget cuts imposed by the Department of Justice. The absence of these facilities has led to unprecedented tension among prisoners, he says.

Dennehy described as "staggering" a decision taken this week to relocate prisoners seeking protection to a drugs detox unit, claiming that the detox facility was no longer available to prisoners wishing to overcome drug habits.

However, a spokesman for the Irish Prison Service said that protected prisoners were only being housed in the detox unit while that unit waited for the next group of prisoners wishing to avail of its services.

One group of prisoners had just completed a detox programme, and the protected prisoners would be moved out of the detox unit as soon as the next group was ready to enter, he said.

Staff at Mountjoy met with management at the prison last week following a serious of violent incidents.

Three prisoners had been stabbed by fellow inmates while one, 21-yearold Gary Douch, died after being viciously assaulted. Douch was murdered in a holding cell in the basement of the prison.

Cells in the basement were designed only as holding cells, but overcrowding in the prison has led to them being used to sleep prisoners unable to be accommodated elsewhere.

Overcrowding in the prison has led to cells sleeping up to four times their recommended number of prisoners. Following the death of Douch, it was recommended that prisoners on protection be housed in single cells. This plan was dismissed as unworkable by the Prison Officers' Association, which says there are not enough cells or beds to implement this proposal.