National says it's "frankly outrageous" the Government is refusing to hold an inquiry into an increase in assaults on Corrections staff.
But Corrections Minister Kelvin Davis says there are plans in place to get on top of the escalating violence behind bars.
The Justice Select Committee, chaired by Labour MP Ginny Anderson, on Thursday turned down National Party corrections spokesperson Simeon Brown's request for an inquiry.
"We've seen a 92 percent increase in assaults on Corrections officers since Kelvin Davis become Minister of Corrections," Brown told Newshub. "It's about time we had a select committee of inquiry to get to the bottom of the reasons why and what needs to be done to reduce that."
Figures show assaults on prison staff have risen rapidly in recent years. Attacks that leave officers needing medical care have nearly doubled, from 158 in 2015/16 to 292 in 2019/20.
Almost all measures of violence against prison staff are going up, despite a declining prison population. Per 100 prisoners, assaults on Corrections officers each year rose from 5.3 per 100 prisoners in 2015/16 to 8.95 in 2019/2020.
Small declines at prisons in Hawke's Bay and Northland were more than offset by huge upswings at Arohata (up 400 percent, from five to 25), Regional Women's Auckland (up 119 percent, from 31 to 68), Christchurch Men's (up 196 percent, from 33 to 98), Manawatu (up 200 percent, from 14 to 42) and Auckland South Corrections Facility (up 233 percent, from 36 to 120).
The most assaults were recorded at Mt Eden and Auckland South, each with 120.
"From my perspective the Government doesn't see this as being a problem," said Brown, saying Davis was more interested in ensuring prisoners were treated well than staff.
"Corrections officers don't get paid to go to work to get assaulted - he needs to take it seriously."
Davis told Newshub "it goes without saying that they deserve to be safe at work".
"The issue of assaults in prisons has been well traversed at the recent annual review.
"Labour members on the Justice Select Committee know that keeping staff safe on the job is a top priority and that Corrections has a plan in place to address this. As minister, I'm also happy to brief the select committee on the progress being made."
Brown told Newshub he'd encourage the committee to take up Davis' offer.
Labour MPs take up five of the nine spots on the committee, the others being held by National (two) and ACT (one).
Davis said Corrections is now "putting in place a long list of actions to reduce assaults and make prisons a safer environment", such as "more training for tactical skills such as de-escalation and retrofitting cell doors with hatches for meal delivery", a particularly risky part of their job.
"I'm also advised that Corrections' leadership and the Corrections Association of New Zealand are working together on what more can be done and I'm looking forward to hearing from them on a joint plan."
Davis has focused on bringing New Zealand's prison population down, saying too many Māori have been incarcerated in the past. It's dropped about 15 percent since the start of 2020, the first significant drop in decades.
There were about 6.6 percent fewer crimes in 2020 than the year before, police data shows, but that is likely to at least be partially because of the COVID-19 lockdown, which saw burglary and theft plummet.