The Chief Ombudsman says Corrections has been disingenuous in interpreting his report into the welfare of mentally ill prisoners, which was released yesterday.
In the report, Judge Peter Boshier highlighted five cases where inmates were restrained most of the day.
In one case, a prisoner was tied to a bed for 16 hours a day, for 37 consecutive days - a total of nearly 600 hours.
Yesterday Corrections chief executive Ray Smith defended the actions, saying staff were trying to save the patient's life.
But Judge Boshier said that was disingenuous, and it was an economic decision, rather than a welfare one.
"Prisoner A was able to be managed when there was sufficient resourcing. The tie-down coincided with the need for the prison to manage its own resourcing. In other words, it was expedient. So I think it is disingenuous to say there was no choice other than to do this."
Meanwhile, Green Party criminal justice spokesperson David Clendon said it was time for a change of culture at Corrections - starting at the very top.
Mr Clendon said given the number and scale of recent scandals involving Corrections, the government needed to ask if it needed to replace the department's leaders.
"The current chief executive has some undoubted qualities, but he has also presided over some serious failures. I always believe accountability should be centred on the top of an organisation, and for that reason, I think there has to be some hard questions asked as to why we ought not to see some changes."