KiwiRail has disestablished 65 jobs in what it says is a bid to help streamline the organisation.
Radio New Zealand News understands that some of those who have already left include Interislander head Thomas Davis, general manager of passenger services Deborah Hume and head of infrastructure and engineering Rick van Barneveld.
The company says not all of the people affected will have to leave the organisation, with some being offered new jobs.
Acting chief executive David Walsh said it was restructuring to try to simplify the company and make it more competitive.
Those who will no longer have jobs would be offered full support.