A senior official with the Prison Officers' Association (POA) has described overcrowding in jails as the worst he has seen in more than 32 years.
Deputy General Secretary Gabriel Keaveny said that around 200 prisoners are sleeping on mattresses on floors, which is "totally unacceptable".
This level of overcrowding only increases levels of violence, he said, along with bullying and intimidation.
Prisons are competing for resources, Mr Keaveny told RTÉ's News at One.
"In the last 12 months alone, we have seen levels of violence against staff increase by 50% in one year. Prisoner on prisoner violence increased by 50%. And where we have had to utilise control and restraint mechanisms - that has increased by 60%."
Mr Keaveny pointed out that the Dóchas Centre at Mountjoy Prison in Dublin was designed for 85 inmates and is now housing over 170.
"There were slight alterations along the way but it's just creaking at the seams," he added.
The Minister for Justice told the POA conference in Galway this morning that the Government will provide more than 400 additional prison spaces over the next five years to accommodate a minimum of 620 additional inmates at Castlerea, Cloverhill, Midlands and Mountjoy prisons.
Simon Harris said there was no silver bullet to fix this overnight, but the promised extra spaces were in addition to other penal reforms.
These include legislation to require a judge to first consider non-custodial and community based sanctions; improving community service; a review of the Community Support Scheme and the Community Return Programme; implementing the recommendations of the High Level Task Force on Mental Health and Addiction and a review of the Fines Act.
But the POA said the Government plans do not go far enough and at least 600-800 prison spaces are needed to deal with the current situation.
"If we had 400 additional spaces now, that would take 200 off the floor," Mr Keaveny said.
"We have certainly 300 or 400 cells doubled up at present. We have doubling up in all prisons across the country."
Mr Keaveny said a consequence of an increased population is more people going to prison and the Department of Justice has not planned properly for this.
He said all possible alternatives, including the reopening of the Curragh prison in Co Kildare and the provision of modular housing at some open prisons, should be examined.
Mr Keaveny also called for recruitment of prison officers to be fast-tracked, saying it takes nearly 12 months for a potential employee to get garda clearance which "is simply too long".
POA concern over 'pack 'em, stack 'em' prison policy
The POA said the level of overcrowding in prisons is putting the lives and welfare of inmates and officers at risk.
Government proposals to appoint additional judges this year will lead to more overcrowding, drug trafficking and serious violence in jails, according to the association.
Its President Tony Power accused the Department of Justice of consistently ignoring the warnings from prison officers and "hoping it will go away".
The POA described the current penal policy as one of "Pack 'em, Stack 'em and Rack 'em", with single cells doubled up, mattresses on floors, and the prisoner population going through the roof with the only solution appearing to be the purchase of bunk beds.
In the Dóchas Centre there were 170 women in custody last week in a prison built to hold 105 - 162% of its original capacity.
During the worst periods of overcrowding, up to five women were sharing a makeshift bedroom.
Pressure is being put on vulnerable prisoners to traffic in contraband including weapons and drugs, while prison officers say they pay the price for the inevitable serious violence that ensues.
Read more: Irish Prison Service confirms overcrowding issues
Last week the Irish Prison Service confirmed that prisons have reached capacity and are overcrowded, following a temporary dip during the Covid-19 pandemic.
As of last Friday, 167 prisoners were sleeping on mattresses on floors, with half of them in Dublin's Mountjoy Prison.
Additional reporting Paul Reynolds
