The Corrections Association says an Employment Court decision allowing for more double-bunking in jails is devastating, and clears the way for more than two people to be put in a cell together.
The court has found the Corrections Department's plan for more double-bunking at four of the country's newest prisons does not breach the union's collective agreement.
Association president Beven Hanlon says the decision is devastating. It means, he says, the department can put as many people as it wants in a cell - at any prison in the country.
Mr Hanlon says the union's lawyer is still reviewing the judgment, but he notes the Employment Court process is not easy to appeal against.
Minister defends practice as safe
The Corrections Minister, Judith Collins, does not accept that double-bunking leads to more violence among prisoners. She says it's already standard practice in 21% of cells, with no ongoing problems.
Ms Collins was responding to the concerns of the prison reform group Rethinking Crime and Punishment, whose director, Kim Workman, says more double-bunking will lead to more rapes and violence in jails.
Mr Workman, a former Corrections Department manager, says the use of double-bunking is already causing extreme emotional stress for inmates, and there's no evidence to suggest that more of it is justified.
Ms Collins says there are cases where lives have been saved by double-bunking, because prisoners with someone else in the cell have been prevented from self-harming.
She says the ruling clears the way for improvements to be made and should ensure there are enough beds in prisons by February 2010. To ensure the safety of staff, she adds, the current prisoner-to-staff ratios will be maintained.