The rail union is set to switch off smart card ticketing systems in NSW, in a move which will cost the state millions of dollars a day.
Opal card readers will be turned off for the afternoon peak from Thursday, after members of the Rail, Tram and Bus Union voted in favour of taking protected industrial action last week.
From 3pm to 7pm every weekday - for an indefinite period - the readers will be deactivated, RTBU secretary Alex Claassens said.
Weeks of private conciliation between the union and the government had achieved little, the union leader told reporters on Monday.
"Everybody is fed up with the ongoing rail dispute, but we've no choice but to continue to do whatever it takes for as long as it takes to force the NSW government to provide safe trains for commuters and fair wages and conditions for workers."
Shutting down the gates around-the-clock was estimated to cost the government between $1.5 million and $2m in lost revenue daily.
It would cost the government an estimated $50m if the shutdown continued for a month.
The union is hoping to create a major headache for the government, while keeping commuters on side.
A possible issue has emerged, with some commuters faced with being overcharged if unable to tap off once machines are shut down at 3pm.
Commuters who do not tap off are charged a maximum fee, as high as the daily cap of $16.80 for an adult.
Those commuters will have to contact Transport for NSW and seek a fare adjustment, RTBU's Craig Turner said.
A Transport for NSW spokesman told AAP deactivating the Opal gates would cause management and operational issues across the Sydney Trains and NSW Trainlink network.
They cited a broad range of concerns, including compromising employee safety, passenger management problems, issues with Park & Ride car parks and the loss of fare revenue.
It's expected the NSW government will launch a Federal Court challenge to the industrial action, although the government let an earlier opportunity to oppose the action within the Fair Work Commission expire.
The move is the latest in an extended and bitter dispute between the government and the union, as the parties try to negotiate a new enterprise agreement after the expiration of the previous one.
They are also at loggerheads over a mothballed fleet of Korean-built intercity trains, which the union says are unsafe to operate.
The union tried to hit the government in the hip pocket by leaving ticket gates open earlier this year.
That was largely unsuccessful, with most commuters continuing to tap on and pay for fares.
Premier Dominic Perrottet last month said people were not interested in the union's tactics and just wanted to get on with their day.
Treasurer Matt Kean has also accused the union of using the travelling public as political playthings.
The NSW transport minister has been contacted for comment.
