Prominent lawyer Nigel Hampton QC has questioned whether a private prison set to open in South Auckland will actually help rehabilitate inmates.
Department of Corrections wants to shut parts of Waikeria, Tongariro/Rangipo and Rimutaka prisons because it says the facilities are too old.
But it said the new private prison will more than make up the numbers of beds lost.
Corrections is aiming to reduce re-offending by 25 percent by 2017 and said it was about half way there.
It said the private prison in South Auckland, which will be run by Serco, will provide the new and appropriate facilities to help reach that goal.
But Mr Hampton said he has serious doubts.
"If profit margin is going to be tight, what's going to be cut first? I suggest the programmes will be the first things that will suffer," he said.
He said a private prison is a business so its priority will be to keep cells full to make money.
"If the profit margin gets too low, the first programmes to be limited or shut down I suggest will be the sort of education, training and rehabilitation programmes because they are the easiest to cut," he said.
"The concerns I suppose are about the reality of how good rehabilitation programmes will be and how long lasting they will be."
The Public Service Association has also slammed the closures and is calling the move privatisation by stealth.
Its National Secretary, Erin Polaczuk agreed rehabilitation may not be at the top of Serco's priority list.
"I have my reservations about whether a company that's running for profit, which the private prisons are, really have the rehabilitation of our offenders at heart and feel a responsibility to New Zealand," she said.
As part of the deal to run the prison, Serco agreed in 2012 that it would perform better than public run prisons, or it would be financially penalised.
Executive director of Re-thinking Crime and Punishment, Ced Simpson, said that means it will work hard to re-habilitate.
"Prisons, of course, are still overseen by the Corrections Department," he said.
"In the case of Serco, their contract certainly ties them into various performance targets in relation to re-integration and reductions of re-offending so we're not concerned on that score."
A spokesperson from Serco said the company is committed to helping Corrections meet its rehabilitation goal by 2017.
260 staff affected
In all, 260 Corrections staff are facing either relocation or losing their jobs, most of those are prison officers.
Serco said there was no immediate chance of any of them being able to work at the new prison.
Labour spokesperson for Corrections, Kelvin Davis, said the job losses were simply not justified.
"These closures are all just to justify the opening of the private prison. They were unnecessary. The government spent something like $900 million during the recession to build the private prison.
"And we're losing 260 jobs from the regions which is a real kick in the teeth for those areas."
Corrections said more than 1000 prisoners from Auckland are currently in cells outside of the city.
Corrections Minister Peseta Sam Lotu-Iiga said that means it makes sense to get as many of them back to the city to be closer to friends and family.