As a KiwiRail safety audit begins on Monday, the Rail & Maritime Transport Union says it is being shut out of important meetings.
The union says it's being blocked from several audit sessions at which it could have worked with management to increase safety.
General secretary Wayne Butson said union representatives want to raise issues such as the scheduling of more trains on the tracks at the same time as workers.
He said this audit - the first under new KiwiRail chief executive Peter Reidy - is the first time employee representatives have been excluded since 2000.
KiwiRail said the union will be involved at the appropriate stages of the audit.