NSW railway staff say they will refuse to work on the state's new fleet of intercity trains from South Korea amid union claims that a "design fault" in the trains increases safety risks.
Projected to cost $2.43 billion, the new fleet is set to replace the V set trains which have been in service for more than 40 years.
The NSW Rail, Tram and Bus Union says a design fault in the new trains means guards are not able to properly monitor passengers in the moments just before the train leave the platform.
The danger period is the 15 or so seconds before a train takes off, when people running late try to board, or when people are separated from children, it says.
The union says the trains' guard's doors and passenger doors close at the same time, stopping guards from monitoring the platform to make sure everyone has boarded safely.
"A design fault in the new InterCity Fleet means they're simply not safe .. It needs to be changed, or we risk serious injuries - or worse," RTBU NSW secretary Alex Claassens said in a statement on Sunday.
Transport for NSW denies there are any issues.
"There is no flaw in the design of the new Intercity Fleet. Traction interlocking on doors, which stops the train from moving while the door is open, is a design safety feature," a department spokesman said.
CCTV on board the train will mean staff no longer have to lean out of the door of a moving carriage to look at the platform, the spokesman said.
"These cameras allow drivers and guards to easily monitor the entire length of the train, even on curved platforms and in bad weather where visibility may be compromised," he said.
The union now says the state's railway workers will refuse to work on the fleet.
"The trains won't be moving anywhere unless these serious safety issues are fixed," Ms Claassens said.
"This design fault is bad for commuters, bad for the train guards, and bad for other workers like the train drivers who are already under immense pressure.
An independent review was commissioned by Transport for NSW of the NSW TrainLink's proposed method for operating the fleet, which was released in December last year.
"The review found the new model is safer than the current train fleet operating conditions for guards," the department's website says.
Static testing of the first two trains has finished and dynamic testing - on the rail network - is underway.