There are warnings plans to force to force prisoners to share cells could endanger the lives of inmates, guards and the general public.
The Government has pledged greater use of putting two people in a cell to cope with an expected increase in the prison population, with Prime Minister John Key saying sharing cells can save money.
The Corrections Department is talking with staff about the prospect of putting two beds in every cell.
Corrections Minister Judith Collins says double-bunking occurs in New Zealand, but an expected increase in the prison population means its use could be expanded.
She says the practice needs careful consideration and though double-bunking would not be appropriate for all prisoners, it is being used successfully in police cells.
Ms Collins says police have found sharing cells has led to less self-harming and requires fewer interventions.
However, former inmate Greg Newbold, who is now an associate Professor of Sociology at Canterbury University, says double-bunking can also create problems.
Dr Newbold says it can endanger prison officers, other inmates and the general public because it creates a more dangerous criminal.
A prison reform group says forcing inmates to share cells could lead to more inmates dying in jail.
Kim Workman from Rethinking Crime and Punishment says New Zealand jails are showing signs of deterioration and double-bunking would make the situation worse.
Mr Workman says sharing cells can increase the risk of rape and assault and makes work more stressful for guards.
He says two men have died in prison in the past month.