NSW court cases will face delays and people planning to visit someone in the state's custody will have to reschedule as prison officers go on strike on Friday.
The strike, which starts at 6am on Friday, is set to run for 24 hours.
The statewide stoppage will affect all areas of the correctional system, and will involve more than 5000 workers.
A Corrective Services NSW spokeswoman said all prisons will continue to operate securely.
"During this period all essential services will be maintained," the spokeswoman said on Thursday.
Corrective Services is also taking legal action.
"We are seeking the assistance of the Industrial Relations Commission to return staff to work," the spokeswoman said.
Prison officers are protesting the upgrading of a charge against one of their colleagues, who shot a man as he tried to escape custody near Lismore Base Hospital in March 2019.
The officer was first charged with manslaughter in February 2021, and pleaded not guilty in February this year.
A trial was set for October, but the officer, who cannot be named, is set to have their charge upgraded.
"All the available evidence in this matter, including newly subpoenaed material, has been reviewed in preparation for the upcoming trial, and the director has determined that the appropriate charge is one of murder," a spokesperson for the office of the Director of Public Prosecutions (DPP) told AAP on Thursday.
The shooting and death in custody was subject to a coronial inquest, which was suspended after a person was referred to the DPP for charges.
Public Service Association general secretary Stewart Little said the upgraded charge coming more than three years after the shooting had prison officers furious.
"Obviously the events have led us now to bring into question how we will use those weapons and how those weapons will be deployed," Mr Little said on Thursday.
"The government needs to absolutely come out and support the very difficult and dangerous work that they do.
"Our union stands with this officer and we will defend this officer."
He said people could make legitimate arguments about the system around prisoner transfers.
"But it's morally wrong to put a single man on trial for a system," Mr Little said.
Corrections Minister Geoff Lee did not answer questions from AAP on Thursday, saying any comment would be inappropriate while the officer is before the courts.
