Sydney trains cancelled due to industrial action, with warning of ‘very difficult day’ ahead

All Sydney trains have been cancelled due to industrial action, leaving thousands unable to make their Monday morning commute.

Workers have been warned to brace for a "very difficult" day by the Sydney Trains chief executive, Matt Longland.

"We're urging customers to obviously avoid travel today or to use the transport journey planner to look for alternative options, such as buses, ferries and light rail if possible," Longland told the radio station 2GB.

Services will be disrupted across the city, including routes connecting Sydney to the Blue Mountains, the south coast and Newcastle. Buses will replace some services but commuters are being told to allow for extra travel time.

Extra buses will be added to the network today, the Transport for New South Wales secretary, Rob Sharp, confirmed early on Monday morning.

"We are doing everything possible to minimise the impact to commuters and sincerely apologise to everyone inconvenienced by this industrial action," Sharp said.

Services were cancelled about midnight last night after negotiations between the Rail, Tram and Bus Union and Transport for NSW broke down, following dozens of meetings.

The parties appeared before the Fair Work Commission twice at the weekend before the state government decided it would be impossible to safely operate services due to planned union action.

"We appeared before the Fair Work Commission twice over the weekend, including at 8pm last night, seeking a stop to this industrial action by the RBTU," Sharp said.

"These actions will impact hundreds of thousands of commuters and come at a time when people just want to get back to work, back to school and back to university - it's not what our community needs at this time."

The RTBU NSW secretary, Alex Claassens, said the planned action - which would see workers only perform the actions they were set without any changes - would have only impacted management, not commuters.

"Workers will be taking protected industrial action, but only transport management will notice the impact, not commuters," Claassens said.

"If commuters see any impact to their services, it won't be because of workers' actions, but because the NSW Government is spitting the dummy and trying to make a point.

"There's no strike - workers are simply performing the shifts we're set without any changes."

The prime minister, Scott Morrison, condemned the action, accusing the union of making it hard or impossible for some essential workers this morning.

"There are people this morning who are going to have an overpriced Uber or they're going to be not able to get to work," he told 2GB. "This is not how you treat your fellow citizens.

"I feel for all of those Sydneysiders today who are affected by the strike."

The groups will be back before the Fair Work Commission later today.