The union that looks after prison officers says the Department of Corrections is covering up to make prisons look safer.
The Corrections Association says the department is fiddling the statistics to mask its failure to keep staff safe as the dangers increase.
Association president Beven Hanlon used to keep statistics on prison assaults on a computer, but says the Department of Corrections blocked his access to the figures so it could hide the truth.
"The Department of Corrections are manipulating figures and definitely not giving a true reflection of violence in prisons," says Mr Hanlon.
Mr Hanlon's figures were significantly different than the Ministry's, which were exclusively obtained by 3 News.
They show in the June year of 2006/07, nationally there were just six serious assaults on staff (when the victim is hospitalised) and 25 non-serious assaults (when there's an injury but no overnight hospital stay).
The Corrections Association based their figures on a calendar year, but recorded a total of 318 assaults.
"Since the mid 2000s we have had trouble retaining staff," says Mr Hanlon. "It's not just about wages, that's obviously an issue - everyone wants to be paid more - but most of it's about safety at work.
"We did a recent survey on our staff, and over 70 percent of our members don't feel safe at work. How can you do our job if you don't feel safe?"
But Corrections disagrees. They say prison safety is improving, its statistics are correct, and serious assaults on wardens are declining.
"Definitely, the data shows over time serious assaults have decreased," says Karen Irwin. "But to us, one assault is too many, so for me and the rest of the department it's pleasing to see the number of serious assaults declining.
"It is still something we are very, very focused on."
Regardless of whose figures can be trusted, the Minister of Corrections says improvements to warden and prison safety are being considered.
"There are no simple or easy answers, but there are ways in which we can improve practise," says Phil Goff, MP. "We are looking at those right now."
However the Department of Corrections has no timeline in place for the improvements, which could include stab-proof vests.
The Corrections Association says that is not good enough.
"A number of prisoners have been killed inside the prison system in the last few years, and so far fingers crossed no officers have been, but unfortunately we believe it's on the cards," says Mr Hanlon.
That is a hand no one wants to see dealt, one of the few issues Corrections and its union seem to agree on.
3 News