The prison officers' union is demanding to know why more has not been done to protect staff after a man has twice been convicted of assaults on female guards while in jail.
Jeremy Mataira has been sentenced to preventive detention after kidnapping and assaulting a guard at Paremoremo prison near Auckland in 2006.
He was already serving preventive detention for the 1991 attempted rape and sexual violation of another female prison officer.
The president of the Corrections Association, Beven Hanlon, says he is disgusted that the Department of Corrections has made no attempt to protect its staff.
Mr Hanlon says that, but for the union, such incidents would go unchecked and would continue to happen.
The department is not commenting on the specifics of Mr Hanlon's claim.
Mataira was sentenced in the High Court at Auckland on Friday.
Mataira kidnapped the guard at knifepoint, took her into a storeroom, bound her wrists and attempted to sexually assault her.
She was rescued by the armed offenders squad.
At sentencing, Mataira took the unusual step of addressing the judge, and spoke of the heart condition he had been diagnosed with just prior to the kidnapping.
He also told the court of his frustration at being in jail, and how he had been misquoted in psychological reports.
However, Justice Hansen said Mataira was manipulative and glib and showed no insight into his offending, nor any willingness to engage with authorities.
Mataira has a long criminal history and has been in jail for almost 30 years.