A union for many of the country's prison officers is accusing the Department of Corrections of misleading the public over which guards will receive stab-proof vests.
The stab-resistant body armour was among new staff safety measures announced by the department in June.
Corrections Association president Beven Hanlon says the vests will only be made available to staff who are putting themselves at direct risk.
He highlights a recent incident he says took place at Christchurch Men's Prison, where a prisoner grabbed a guard by the head and slashed at his neck with a razor blade melted into a toothbrush.
Mr Hanlon says when another prison officer responded to the incident, she was punched in the face and pulled to the ground by the hair.
He says neither of the guards assaulted would qualify for a vest, as it would only be issued after the incident, when the prisoner had to be removed from the area.
Mr Hanlon says guards at Auckland Prison were told on Monday the stab-proof vests would now go to officers doing vehicle checks, which is contrary to earlier reports.
The Corrections Department says guards at Auckland Prison's maximum security unit will have access to stab-resistant body armour but the vests will not be standard issue.
The stab-proof vests and other protective equipment will be handed out at several prisons over the next six months.
Assistant general manager for prison services Brendan Anstiss says staff in maximum security units will get the armour though guards will not be wearing the vests all the time.
He says few countries provide prison officers with body armour as a matter of course.
The department says the extra equipment and additional training for staff will cost more than $4 million.