Union members are bearing the brunt of commuter frustration over train breakdowns in and around Wellington.
KiwiRail says a number of problems have recently led to an "increasing workload" for its maintenance depot.
Commuters have told Radio New Zealand of ongoing and persistent signal failures, delays and operational hold-ups - which often occur without explanation.
The Rail and Maritime Transport Union says its members are fielding a "large number of complaints" from passengers.
General secretary Wayne Butson says they are angry at breakdowns and cold from broken heating units.
Wellington is awaiting the arrival of a $235 million fleet of 96 new electric commuter trains, which is due to arrive from Korea in the middle of next year.