Some Auckland trains are running behind schedule, further delaying commuters' morning trips, due to a temporary timetable change caused by train staff refusing to work overtime.
The industrial action - which is set to last for three weeks - coincides with the start of the busiest period for public transport as students return to university.
It was standing room only on the trains heading into the city this morning.
Some workers and students said they would now be late and they were considering alternative arrangements for the three weeks of the new timetable.
One woman said a co-worker at Ellerslie station couldn't get on two trains becuase they were too full.
Trains on the Southern, Eastern and Western lines are now scheduled to come every 20 minutes at peak times.
The Onehunga and Pukekohe weekday train services will have the usual timetable. Bus and ferry services are not affected.
Auckland Transport said there will be more carriages, so each service would hold up to 900 passengers.
But it said 10,000 people use the train service between 6.30am and 8.30am in the morning and 4.30pm and 6.30pm in the afternoon.
Auckland Transport said there were more buses running and some people may be able to travel at off-peak times.
The Rail and Maritime Union said it had safety concerns about a proposal to give train drivers the responsibility of opening and closing doors.