The Rail, Tram and Bus Union has planned strikes and other actions throughout August.
"People are in my office talking about a calendar for September," RTBU NSW secretary Alex Claassens said.
"Everybody is very frustrated and angry and something's got to give here."
It came after workers refused to operate 37 trains they said did not meet minimum maintenance standards, leading to delays on the T1, T2, and T8 lines on Monday.
Mr Claassens said trains that did not meet minimum maintenance standards could be affected by a range of issues "from safety all the way through to cleanliness".
He blamed outsourcing and extended time between maintenance inspections for failure to meet standards.
"The issue with these (Waratah) trains is that they're not serviced on a monthly basis as all of our old ones were," Mr Claassens said.
Meetings took place on Friday, Sunday, and Monday to try and resolve the long-running dispute over a new enterprise agreement and the union's safety concerns with the mothballed Korean-built fleet of intercity trains.
Train services will be less frequent on Tuesday between 10am and 4pm on the Blue Mountains and Newcastle lines, affecting stops from Newcastle to Lithgow.
Sydney's City Circle line will be affected when workers stop work from 10am to 4pm on Thursday.
Mr Claassens said trains will still run, with workers brought in from elsewhere on the network.
Premier Dominic Perrottet said trains being out of action was incredibly disappointing and dismissed the industrial action the union has been engaged in throughout this month as "political games".
He said Monday's action was "unplanned", although the union advised weeks ago it would not be operating trains that did not meet minimum standards.
The premier said the trains did meet those standards.
"This is just the union once again taking action and inconveniencing people for their own political benefit," he said.
While the action that took trains out of service on Monday was in the union's advised calendar, Mr Claassens said the union did not expect so many trains would not meet the standards.
"None of us understood that it was going to have that massive impact, and that again has highlighted the problem that we've got," he said.
He denied the industrial action had anything to do with politics, saying the union and Labor party have a long history of "massive fights".
If the union is playing political games, the government and opposition appear to be on the same team.
NSW Labor leader Chris Minns was calling for this week's two planned strikes to be abandoned on Monday.
"I don't think further industrial action will motivate the NSW government to make any further changes," he said.
"Whatever progress has been made needs to be banked and the two sides need to get back to the negotiating table ... further industrial action will only see commuters be the meat in the sandwich," he said.
The union gave feedback on a deed to change the new intercity fleet provided on Thursday and received a revised draft on Monday, although it is not the same one Mr Claassens signed in June.
The government wants signing the deed contingent on a new enterprise bargaining agreement. The union wants them dealt with separately.
The trains have been in storage since 2019 and the enterprise agreement expired in May 2021.
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