Corrections officers' safety could be at risk if a report into the 2013 riot at the Spring Hill Corrections Facility is not made public soon, Labour's Jacinda Ardern says.
But Corrections Minister Anne Tolley said the report is being finalised and she has not read it yet.
The inquiry will cover the causes of the June 1, 2013, riot at the prison, which involved 29 prisoners who ran free in the courtyards of two cell blocks, lighting fires and damaging facilities for more than eight hours.
Three Corrections staff were left with broken bones and two prisoners with undisclosed injuries.
It was estimated that damage done amounted to $14 million.
Tolley said court action against the accused inmates "will guide when it [the report] can be released. Some sections may be retained for obvious security reasons".
But Ardern said the delay surrounding the release of the report was "strange".
"We've been stonewalled on this and other issues. This is one particular report that was instigated after a very serious incident and I would have thought that to ensure that this doesn't happen again and to ensure the safety of corrections officers across all sites," she said.
"Having this report out sooner rather than later is necessary."
Tolley said Ardern's criticism was "ill-advised".
"I would say that the law, and the security of our prisons, is more important than the ill-advised politicking of a Labour MP."
Corrections Central Regional Commissioner Terry Buffery could not comment on the report because of court action against the accused inmates. But a statement made by chief executive Ray Smith last year provided an insight into what they had found. "Our view is that the primary cause of the riot was the actions of a group of violent prisoners with gang associations who had become intoxicated on a fermented fruit-based concoction, and [who] had been fighting earlier in the day."
Smith's view differed from a source who told the Times last year that the riot was due to the lockdown regime introduced by prison managers.
- Waikato Times