The NSW Ombudsman's report on prison punishment in the past five years found widespread substandard, non-compliant and sometimes blatantly unlawful processes.
Inmates whose behaviour warranted mental health support were instead disciplined, people were punished twice for the same matter and staff frequently used "last resort" penalties banning family contact.
The report found about a third of the 10,000 internal offences unrelated to drugs each year could be invalid.
Further criticism was made of the "inherently unfair" lack of appeal rights.
"It is nothing short of maladministration," the Greens' Sue Higginson said. (Jono Searle/AAP PHOTOS)
It's another troubling set of findings about NSW prisons after a scathing inquiry in March found a serial rapist prison guard was protected by management unwilling to investigate rumours, triggering the departure of the state's prison chief.
"When an officer metering out disciplinary measures becomes the police, the prosecutor, the judge and the jury, it's clear that any semblance of procedural fairness and accountability has gone missing in action," Greens justice spokeswoman Sue Higginson told AAP.
"The state is running a kangaroo court system in what is meant to be an internal justice system for some of the most vulnerable and disempowered people in NSW.
"It is nothing short of maladministration."
Ms Higginson described Corrective Services NSW as a "renegade arm" of the state.
In one case detailed by the ombudsman, inmate Tina was awaiting trial when charged with failing a drug test.
She was not referred to a drug and alcohol program, despite her recorded pleas and prison policy mandating a referral.
"You know I have been asking everyone to help me," Tina, a pseudonym, said during a disciplinary hearing.
Corrective Services NSW put the non-referral down to a rule that it could not force remand prisoners into drug and alcohol programs.
That failed to explain why a statewide policy to refer all inmates, willing and unwilling, was not followed, the Ombudsman said.
Young Aboriginal men and women were also confined alone as punishment, contrary to policy and the findings of the 1991 Aboriginal deaths in custody royal commission.
A second report focused on a prison run by British multinational Serco found staff unlawfully used collective punishment after a colleague was violently assaulted in a locked officer station in September 2023.
A few bystanders clapped the violent assault's perpetrator afterwards but dozens more were penalised "contrary to law" for matters such as walking over a red line, the ombudsman found.
Serco then cut off 175 inmates in the prison unit from the rest of the prison for five days, conduct the ombudsman found was "unreasonable and oppressive".
The multinational has been urged to apologise to all 175 inmates bar the perpetrator.
In a statement to AAP, Serco highlighted that their staffer remained unfit to return to work almost a year on.
Changes to prison management are being implemented immediately, Anoulack Chanthivong said. (Bianca De Marchi/AAP PHOTOS)
But it said it regretted its later actions were "not up to standard" and it was implementing key recommendations.
Corrections Minister Anoulack Chanthivong said the reports raised significant issues about prison management and changes were being implemented immediately to reduce risk of invalid disciplinary decisions.
A wider reform of Corrective Services includes separating it from the justice department, allowing the minister to appoint - and sack - the prison chief.
"We're also getting on with changes to update and restore trust in our prison network," he told AAP in a statement.
"That includes reviewing the current legislation, staff training and disciplinary processes that are in place."
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