Sydney’s ongoing train drama is expected to worsen before it’s resolved after the union indefinitely banned overtime work.

The ban will come into effect next Thursday, following the state government’s refusal to negotiate fair pay, according to the Rail, Tram and Bus Union.

New South Wales union secretary Alex Claassens said drivers were forced into the position.

“We know that it will hurt them, but at the same time, we don’t want to hurt the commuters; we don’t want to damage the system,” Mr Claassens said.

Commuters will be kept up-to-date and “the last thing any railway worker wants to do is inconvenience commuters”, he said.

“I actually feel sorry for the commuters. This is a situation that has been brought on by our transport minister and his bureaucrats.”

He said rail workers had been doing excessive overtime, leaving drivers “fatigued and exhausted”.

The industrial action is unrelated to the recent scenes on the train network, but could worsen delays.

A Sydney Trains spokesperson said the department “will do everything possible to minimise disruption and already have a number of contingency plans in place”.

“We remain committed to finding an agreement that is beneficial for everyone but it is important our customers are not disrupted during these negotiations,” the spokesperson said.

“We look forward to further negotiations in the coming days to try find an agreement.”

Sydney Trains boss Howard Collins earlier on Monday said there could be fresh chaos on the rail network if drivers refused to work unplanned or rostered overtime.

“That will have an impact on the network,” Mr Collins told reporters.

“It would be an important challenge for us and we would have to reschedule [services].”

NSW Transport Minister Andrew Constance said he was “deeply disappointed” by the industrial action.

Rail workers are fighting for an annual 6 per cent pay rise over four years. The government insists any pay demand must be within the 2.5 per cent cap for all public sector employees.

Mr Claassens said all public sector employees were worth more than 2.5 per cent, not just rail workers.

The transport minister will try to make us sound greedy – he always does – but I don’t think anyone is going to buy that, especially given the chaotic scenes of the government’s making this past week.

He said pay negotiations had dragged on for six months without success because the government had not co-operated.

Union members will also be wearing union paraphernalia and be carrying campaign material from this Friday as part of the action.

The industrial action is unrelated to the new train timetable rolled out by the government in November, which added services but worsened staffing pressures.

It comes after Premier Gladys Berejiklian apologised to commuters caught up in last week’s chaos and admitted more should have been done ahead of time to prevent the meltdown.

“I want to wholeheartedly apologise to all of our customers. The system most days is world class and some days, unfortunately, we let commuters down,” she said.

Ms Berejiklian revealed that if “permanent tweaks” were needed to Sydney’s new more intensive train timetable “then we’ll make them”.

Mr Claassens said the union earlier flagged the new timetable was rushed and had “begged for help”.

The union will meet with management on Tuesday to discuss the timetable, and will meet with Mr Collins on Thursday to continue enterprise negotiations.

Thirty-six train services scheduled to run during peak hour on Monday were cancelled to avoid a repeat of last week’s debacle that left thousands of passengers stranded.

Buses were on hand to supplement reduced services.

Travellers on the busy North Shore line also faced delays due to urgent signal equipment repairs at Milson’s Point.