Premier Dominic Perrottet was briefed on the dispute, which revolves around the government's new intercity fleet, by Employee Relations Minister Damien Tudehope on Tuesday night.
"My understanding is there could be some positive developments today," he told reporters on Wednesday.
Rail, Tram and Bus Union secretary Alex Claassens said progress had been made on a deed guaranteeing changes to the Korean-built trains, which the union says aren't safe to operate.
He expects to be presented a deed shortly, which will be reviewed by the union's lawyers and delegates.
"At that point, I suppose they will legitimately be able to say to me, 'can you look at postponing your industrial action?'" he told reporters on Wednesday.
That will take at least 48 hours, meaning Thursday's planned strike for workers on the City Circle and Redfern station will go ahead.
Suburban trains will run to a reduced timetable on Thursday, with workers coming from other parts of the network to plug gaps left by striking colleagues.
The government could head off more action planned for next Wednesday, when drivers will refuse to operate overseas built trains, if it gets the union a deed by the end of the week.
Mr Perrottet says the government has committed to making changes to the fleet, although he continues to maintain they aren't necessary.
Mr Claassens said the union had no reason to take him at his word.
"We just can't accept a verbal confirmation anymore."
The union had been promised changes numerous times over several years, he said.
Another meeting took place on Wednesday, the fifth since Friday, with the RTBU joining other unions in enterprise agreement negotiations.
The government wanted to make the deed for the changes contingent on finalising a new enterprise agreement after the old one expired more than a year ago, however the RTBU is not the only union whose members the agreement will cover.
The trains the union wants changed were designed for drivers to monitor platforms via CCTV, but there is a risk a driver would not be able to see if someone had fallen through the gap between platform and train.
Retaining the guards who monitor platforms as trains approach and depart also secures their jobs.
Driverless trains are used on the Sydney Metro, but it was specifically designed for them, and the platform is separated from the tracks with automatic doors that open when the train doors open.
More than 30 trains were out of action on Monday, when the rail union refused to operate trains that did not meet minimum maintenance standards.
Mr Claassens said those trains could have had dangerous safety issues while others could have simply been vandalised.
"None of us expected this many trains to fail to meet that standard," he said.
On Tuesday, industrial action delayed and reduced services on the T1, T7 and T9 lines and prevented the T5 line from operating.
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