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Auckland's passenger rail services face disruption this afternoon because of train crews' threat to stop work over concern about assaults on workers.

The Rail and Maritime Workers Union has called a stopwork meeting from 2pm to 5.30pm of more than 200 members, which will mean chaos for homebound commuters unless train operator Veolia Transport averts the stoppage by offering improved security for staff.

The stopwork call follows a series of attacks, the latest an assault and robbery on Tuesday night of a female train manager in sole charge of the carriages of a train by two offenders at a western line station.

She has been off work since the attack. The union says it does not want to disclose its severity or identify the station, for fear of compromising police inquiries.

Union organiser Todd Valster said yesterday another crew member was assaulted last week, and there was an average of one attack a month on Auckland rail workers.

That was despite frequent requests to Veolia for greater protection, notably an extension of coverage by Maori wardens, who are contracted to ride on most but not all trains from 8pm each night and while children are travelling to and from school.

A major problem was a lack of a communication system between locomotive drivers and staff in the carriages.

Mr Valster said the stopwork would proceed unless the company responded positively at a meeting this morning to the union's proposals for the protection of its staff in compliance with its legal obligations.

Veolia managing director Graham Sibery said last night that the company deplored the latest attack, which was one of eight in the past year, and was keen to take all practical steps to prevent recurrences.

He hoped progress in this morning's discussions would allow the trains to keep running.

The Auckland Regional Transport Authority said it was notifying passengers by text messages and on its website that train services may be disrupted this afternoon, and that they may wish to make other travel arrangements.

Auckland Regional Council chairman Mike Lee acknowledged concern about violence against rail workers, but said the union had never approached him about any safety concerns. He urged it to call off the stopwork meeting.

"I am more than willing to help them get some protection for their members.

"But it would be absolutely reckless and disruptive to hold the whole network to ransom and inconvenience thousands of innocent law-abiding Aucklanders because of one or two bad eggs."

Union general secretary Wayne Butson called Mr Lee's comments outrageous.

"I would like to think that Mike Lee ... would be equally concerned about the safety of public transport staff as he obviously is for the commuters," he said.

"This is not being done to deliberately inconvenience Auckland commuters - it is the only way we can get all our members together in one place at one time - and that requires the stopping of trains."