The long-running stoush between the NSW government and the rail union will take trains off the tracks again this week.
Commuters could be affected for several hours on Wednesday when the Eastern and Illawarra line will be out of action.
It means trains from Bondi Junction to Bomaderry won't run on Wednesday.
Other services may run to a reduced timetable.
The Rail, Tram and Bus Union is staging protected industrial action as it seeks to secure changes to a new fleet of intercity trains and reach a new enterprise bargaining agreement.
The new trains have been sitting in storage since 2019 and the previous enterprise agreement expired more than a year ago.
The union has already banned transport officers issuing fines and the industrial action will be escalated to include a six-hour strike on Wednesday between 10am and 4pm.
The RTBU said about 90 per cent of train crews would still be available to work, and blamed the government for shutting down the Illawarra line.
RTBU secretary Alex Claassens said the action had been designed so services could continue.
"There is absolutely no reason for the Illawarra line to be shut down on Wednesday," he said.
"If it is shut down, it will be because Transport bureaucrats have simply decided they don't want to run the trains, not because they can't."
The action was supposed to cause headaches for management, not commuters, he said.
The union has planned area-based strikes three more times before the end of the month, and will also leave station gates open and refuse to operate foreign built trains on some days.
Transport for NSW has been contacted for comment.
