Sydney commuters have been urged to avoid public transport on Tuesday as a four-hour strike from 9am will cause major disruptions and delays throughout the network.

Unions say they planned for weeks especially around getting essential workers to and from work.

Sydney Trains and NSW TrainLink networks will be replaced by extra buses, ferries and coaches that still operate under COVID-19 capacity limitations.

The strike comes amid negotiations for a new enterprise agreement, which the parties remain at loggerheads over pay and conditions.

Sydney Trains chief executive Matt Longland said he had been proud of the transport workers' efforts during the pandemic so it was poor timing for a strike.

"Our frontline staff has done an amazing job during this COVID period to keep services operating safely," he said.

"We are very disappointed that they've taken this action because we know that essential workers rely on rail services to get to work every day."

NSW Trains chief executive Dale Merrick said he respected employees' rights to take industrial action as part of enterprise bargaining.

"But we would say it's not the right time," he said.

The union says senior officials have refused to sit down and fairly negotiate since the enterprise agreement expired in May.

"Mr Longland and Mr Merrick, they came out for a press conference this morning but have refused to have conversations with us," Rail, Tram and Bus Union NSW secretary Alex Claassens told AAP.

"'They say they're bargaining in good faith, but they are not as they've refused to come to our meetings."

Train drivers on Tuesday will participate in a workplace Zoom meeting to discuss next steps and work out whether further strikes will take place in the next 30 days.

Industrial action began three weeks ago in subtle moves that looked after essential workers but still indicated "we're not happy", Mr Claassens said.

The union is asking for a 3.5 per cent wage rise while the NSW government is offering 0.3 per cent for the first year of a new enterprise agreement.

Other issues include restructuring people into other roles, outsourcing of COVID-19 cleaning roles, and the absence of mandatory on-site virus testing.

Mr Claassens said if chief executives continued to send junior personnel in their place into meetings, reiterating the same old script, "this stuff will continue until it's worse and worse".

Australian Associated Press