The Attorney General's Department says it will be "business as usual" at Perth's central law courts on Monday despite a planned strike by 130 security officers.
Security staff employed by G4S custodial services will strike for 24 hours at the District and Central Law Courts over pay negotiations stalled since February this year.
The workers' enterprise bargaining agreements reportedly expired in June.
The Transport Workers Union says G4S staff are paid less than their regional counterparts employed by private contractor SERCO and this could be the first of many strikes if workers' demands are not met.
"They have a very very hard job, they're dealing with hardened criminals some of the time, and they believe they're not being paid fairly," Transport Workers Union secretary Paul Aslan said.
Mr Aslan said G4S was offering pay increases only if service pay for long-serving staff was removed, which he said could hit the hip pocket of more than 50 percent of employees.
"It's taking with one hand while giving with the other," he said.
The strike was originally scheduled for two weeks earlier but Fair Work Australia delayed the action to allow the courts to put alternate security measures in place.
In an emailed statement Executive Director of Court and Tribunal Services Ray Warnes said the department has a contingency plan in place but will not comment further on arrangements for security reasons.
Mr Aslan said he was "surprised" the courts would stay open and perhaps the department was going to use 130 police officers.
"I don't know how you can do that because they won't have the people to man the courts, I will be very surprised if it was business as usual," he said.
"Certainly it is going to be very inconvenient for everyone concerned."
Contracts Manager for the Perth office of G4S Karen Marlow said she had no comment on industrial negotiations.The central, eastern states branch of global security firm G4S has also been contacted for comment.
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