More than $1 million of taxpayer money has been spent on 193 slushy machines in a bid to keep prison guards cool over summer.
Opposition leader Simon Bridges has called out the Government, saying it's "irresponsible" and "wasteful" spending.
But Corrections Minister Kelvin Davis has reportedly said he didn't care what Bridges had to say and he supported the health and safety spend.
Documents released to National under the Official Information Act revealed Corrections spent $1.095m on 193 ice slushy machines at the end of last year.
Corrections say the flavoured crushed ice drinks are for the wellbeing of staff and not for inmates.
Corrections acting national commissioner Andy Milne said their staff, of more than 9000, worked tirelessly to manage an increased number of prisoners in hot and confined spaces and conditions.
During the summer of 2017/18 New Zealand experienced significantly higher temperatures than usual, with Wellington recording its hottest January since records began in 1927, Milne said.
He said the heat caused "significant discomfort" for staff and had the potential for significantly increased prisoner tension and aggression.
"In preparation for the 2018/19 summer and the potential repeat of the previous summer's conditions, we provided crushed mix mixture for staff to consume when required to reduce core body temperatures in excessive heat conditions," Milne said.
Research shows the machines offer an immediate and effective means of significantly reducing core body temperature in most situations, up to three times more effective than water, Milne said.
Chief custodial officer Neil Beales said the feedback he'd had was that the investment in the machines has been appreciated by staff.
"These actions, combined with the efforts of our staff, were effective – with no major incidents occurring despite the conditions," Beales said.
Bridges said this "frivolous spending" followed the Government's Justice Summit which saw $1.6m including $20,000 on three registration desks, $970,660 on consultants, $26,592 on MCs, $65,800 on gourmet catering and $101,528 on international speakers.
"Government departments under Labour have got the idea that taxpayer money is there to spray around on whatever. Corrections Minister Kelvin Davis owes New Zealanders an explanation and an apology.
"This kind of spending shows the Government doesn't need to be taxing Kiwis more, as they clearly don't know how to spend what they're already taking," Bridges said.