Transport agency Waka Kotahi says one of the Te Huia trains that crossed a red light could have crashed into a busy commuter train.
The rail service connecting Waikato and Auckland has been caught running at least two stop signals.
Now, it's banned from entering Auckland's central area.
Passengers have to get off in Papakura and catch a bus if they want to go into town.
Operator KiwiRail declined to be interviewed this morning.
Waka Kotahi director of land transport Neil Cook spoke to Corin Dann.