Dozens of prison guards have walked off the job in Darwin over the Northern Territory government's four-year public sector pay freeze.
The protected 24-hour strike on Monday is also protesting the alleged under-resourcing of the sector, with the union saying it is in crisis.
About 60 officers from the Darwin Correctional Centre in Berrimah started strike action about 7am. They will return to work at 7am on Tuesday.
United Workers Union NT Secretary Erina Early said the government needs to offer a fair wage increase to offset the rising cost of living and the risk officers face on the job.
"Corrections continue to be at crisis levels with overcrowding, lack of staff, an inadequate budget," Ms Early said in a statement.
"Officers are suffering and we need to ensure they are properly remunerated for the risk they deal with on a daily basis."
Ms Early said corrections officers would take further industrial action if the government did not "return to the table with a reasonable offer".
"I urge the government to consider the long-term impacts of their four-year wage freeze," she said.
The NT government said prisoners would be confined to their cells during the industrial action and youth justice officers from Don Dale Youth Detention Centre would help staff the prison.
"NT Correctional Services' top priority is the security, safety and wellbeing of all prisoners, employees and the wider community," Attorney-General and Minister for Justice Chansey Paech said.
"Contingency plans are in place to ensure core functions are maintained, including the delivery of meals and medications for prisoners, and the availability of staff to respond to incidents and emergencies."
Monday's industrial action follows on from earlier work stoppages in Darwin and Alice Springs in May.
The pay freeze for more than 20,000 public servants was introduced in November 2020 in a bid to save more than $400 million amid ongoing territory government deficits and climbing debt levels.
It was accepted by 57 per cent of employees.
The Darwin Correctional Centre is a minimum to maximum-security prison for men and women. It has a capacity of about 1250 prisoners.
On July 17 there were 1201 prisoners at the facility, including 1118 men and 83 women.
Social and professional visits have been suspended during the industrial action.
