Auckland rail workers will start voting next week on whether to take more industrial action over a reduction in staff.
They have been in collective bargaining with Transdev since May, and went on strike early last month.
Rail and Maritime Transport Union workers are against plans to do away with train managers and operate driver-only trains.
Organiser John Kerr said an example of why train managers are so vital was last Sunday, when a baby got clipped by a train at Meadowbank Station.
Without the train manager there, the driver would have had to manage that emergency all by himself, he said.