The 24-hour action on Wednesday will cause major disruption to services as those trains make up about 70 per cent of the fleet.
Sydney Trains chief executive Matt Longland advised train commuters to avoid unnecessary travel and work from home if possible.
Most timetables will be reduced to a 30-minute frequency, however no services will run on the T5 Cumberland and T7 Olympic Park line.
Multiple unions are involved in ongoing negotiations for a new enterprise agreement to replace one that expired in May 2021.
A separate fight 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 is closer to a resolution.
A letter from the government to the union on Sunday said it would drop its request to make a deed for alterations dependent on a new enterprise agreement being finalised if the union abandoned Wednesday's action.
It said it would authorise the work to begin as set out in a deed of agreement between the union and government.
The Rail, Tram and Bus Union (RTBU) wrote back saying the offer lacked clarity and was unacceptable because it had not seen the deed and did not have the authority to make decisions on behalf of the other unions involved in the enterprise agreement negotiations.
RTBU NSW secretary Alex Claassens dismissed 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.
The union has promised to suspend further industrial action throughout September if the government agrees to execute Friday's deed, as well as other demands for job security and increased wages in the enterprise agreement, back paid from the enterprise agreement's expiration last year.
"Obviously the thing that everybody wants is more money. We need to have that conversation," Mr Claassens said.
NSW raised its public sector wages cap to three per cent this year and could raise it to 3.5 per cent next year, however Mr Claassens said the cap does not apply to rail workers.
"It's never applied to us … because we're in the federal system," he said.
The union sought a response from the government by 5pm on Tuesday.
Premier Dominic Perrottet said the industrial action throughout August was "politically motivated".
"It's been ongoing now for a substantial period of time," he said in Victoria on Tuesday.
"(The Labor opposition) has also said the strikes must come to an end. There's a unity ticket here," he said.
Opposition Leader Chris Minns repeated his call for the union to abandon its industrial action.
"Further industrial action is not going to drive the NSW government to a conclusion," he said.
"(The union) have got every right to progress their claims. I think that can be done around the negotiating table, rather than via strikes."
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