Train drivers will begin four days of action on Tuesday by limiting trains to a maximum of 60km/h.

Transport for NSW warned intercity travellers and those using long distance regional services to limit travel to essential trips only.

"A significant reduction in Intercity and regional services to the Central Coast, Newcastle, Hunter, Blue Mountains, Southern Highlands and South Coast lines is also expected on Thursday 30 June and Friday 1 July," Transport for NSW said in a statement on Tuesday morning.

Meanwhile, hundreds of workers from 80 hospitals are expected to take part in a mass meeting in central Sydney on Tuesday afternoon.

Transport for NSW says commuters can expect significant disruption to rail services as delays and cancellations increase during the week.

Suburban trains are expected to run on an amended timetable, with regular services cut by half during the peak period.

Alternative travel arrangements will be made where possible.

Nurses will walk off the job for various hours in defiance of the Industrial Relations Commission.

NSW Nurses and Midwives Association acting general secretary Shaye Candish says the meeting comes after pleas to increase staff numbers to deal with extreme workloads fell on deaf ears.

"There's widespread dissatisfaction amongst our members over the NSW government's refusal to even consider safe staffing ratios," she said.

"The government is continuing to ignore the pleas of highly skilled clinical professionals who remain extremely worried about the delivery of safe patient care now and into the future," she said.

Nurses want a nurse-to-patient ratio of one to four on hospital wards and a midwife-to-patient ratio of one to three.

The action by The Rail, Tram and Bus Union will escalate until Friday when drivers refuse to drive foreign-built trains, reducing the capacity of the fleet to just 30 per cent.

The action is driven by safety concerns over new Korean-built trains, which the union maintains need to be modified to keep passengers safe.

On Thursday public and Catholic schoolteachers will strike for 24 hours over pay, with the unions saying teachers are grappling with unsustainable workloads and worsening staff shortages.

Premier Dominic Perrottet said unions organising illegal strikes should cop steep penalties.

The government wants to impose maximum fines of up to $55,000 for the first day of illegal industrial action and $27,500 for each subsequent day.

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