The government and the rail union are blaming each other for the 24-hour strike on Wednesday, which will sideline foreign-made trains that comprise about 70 per cent of the fleet.
Sydney Trains chief executive Matt Longland is advising commuters to avoid all unnecessary train travel and work from home if possible.
Train services will be reduced to about a 30-minute frequency on most lines, he says.
The T5 Cumberland line and and the T7 Olympic Park line will not have any services.
"Avoid all unnecessary (train) travel and leave the capacity that is available on trains for those that really need it," Mr Longland told Sydney radio 2GB on Tuesday.
"Work from home or avoid the trip on the train tomorrow."
Rail, Tram and Bus Union NSW secretary Alex Claassens is promising the month of targeted rolling stoppages and bans will be suspended on Wednesday and says September will be free of industrial action on the NSW rail network.
"We've actually guaranteed them peace until the end of September, or until the enterprise agreement gets voted up, whichever comes first," Mr Claassens said on Tuesday.
Multiple unions are involved in the negotiations for a new enterprise agreement, to replace the one that expired in May 2021.
A separate fight continues over modifications to a fleet of mothballed Korean-built intercity trains the union believes are not yet safe to operate in the NSW rail network.
The government sent a letter to the union on Sunday dropping its request to make alterations to the trains dependent on a new enterprise agreement being finalised, and calling on the union to abandon Wednesday's action.
The government's insistence the agreement be locked in before the modifications begin had been a sticking point in the protracted negotiations.
A deed for changes to the train was negotiated further on Friday, but Mr Claassens said he had not been presented a copy to sign on Monday, dismissing the government letter as a stunt.
"It was a letter that was clearly designed for a purpose but it wasn't designed for resolving our dispute," he said on Tuesday.
Transport Minister David Elliott said he was disappointed by the union's assessment of the letter.
"It was not a stunt. It's exactly what the rail union asked for," he said on Monday.
"Just take the deed ... we've given you what you wanted."
Mr Claassens said the union had made minor modifications during negotiations on Friday but did not receive confirmation the deed was suitable.
"Instead ... we've been forced into another round of lengthy talks rather than getting on with the job of getting a signed deed which we can take to members and delegates to consider," he said.
Negotiations are continuing.
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