Dozens of prison guards protested outside Mt Eden Prison in Auckland on Saturday against plans to privatise some of the country's jails.
More than 60 prison guards chanted slogans and held placards saying 'Stop The Cell-Off' and 'No Profit From Crime'.
The Corrections Association, the union representing prison guards, says legislation currently before Parliament would lead to the private management of as many as five prisons.
Association president Beven Hanlon says New Zealand has one of the best prison systems in the world and privately run facilities will not deliver the same standards.
"We have low levels of escape, we have low staff-to-prisoner ratios which means we've got really low costs and we've got low suicide rates - and believe it or not we've got improving rehabilitation rates.
"These private companies cannot deliver what we're delivering," he says.
Mr Hanlon says if prison management is privatised, guards will face the prospect of losing their jobs, only to be re-hired at reduced wages and under poorer conditions.
Australian experience negative
Mr Hanlon cited the example of a a prison in New South Wales, Australia, that was taken over by a private company and has since had guard numbers reduced by a third.
"There's a prison there that operates with 95 staff. They've just been taken over by a private company and going to open with 60 - the same amount of prisoners, a third less staff."
In addition, he says the remaining officers will have their pay cut by 20%.
"That's a big whack to any community."
The Chairman of New South Wales prison officers union, Matt Bindley, joined the protest.
He says privatisation would have a particularly bad impact in New Zealand, because the likely location of the new jails would mean people would have to relocate, or start their lives again in another industry.
"The impact on society is also going to be great, because the money is not going to go into society that normally would."
He says privatising jails would cause a great upheaval "for no other reason than to put money in the shareholder's pocket".
The Corrections (Contract Management of Prisons) Amendment Bill has passed through the select committee stage.
Mr Hanlon says more protests are planned around the country.