Auckland's new trains could be running at full speed by the end of the week, Auckland Transport says.
Drivers have complained the new electric trains have had their speed capped to slower than the fleet they replaced.
A $600 million train fleet is being introduced to encourage more commuters to use rail but in some areas they are 10km/h slower than the old fleet.
Auckland Transport Group Manager for Public Transport Mark Lambert said the speed cap was a safety precaution while drivers got used to the new trains, and he hoped to lift it in a matter of days.
Regional organiser Stuart Johnstone said drivers were frustrated and the union would meet Transdev, which operated the trains, on Thursday to ask for changes.