Those wanting to travel on the Interislander ferry will need a COVID vaccine pass or a recent COVID-19 test to take the trip across the Cook Strait.
From December 15, the test or pass requirement will be needed for those 12 or older.
The KiwiRail announcement comes just hours after Prime Minister Jacinda Ardern announced the country's planned move to the traffic light system, also known as the COVID-19 Protection Framework.
Interislander general manager Walter Rushbrook says they have adopted the same policy used by Air New Zealand for their domestic flights so passengers can have a consistent travel experience, regardless of whether they travel by sea or air.
Rushbrook says passengers will need to provide proof of their vaccination status or proof of a negative COVID-19 test when checking in.
He adds the inter-island ferries are a key passenger and freight connection between the North and South Islands, and they are expecting the services will be very busy this summer, with people travelling around the country to enjoy holidays and spend time with friends and family.
Staff working aboard Interislander ferries will also be required to be double-vaccinated or receive a negative test every 72 hours, with staff needing to have their first dose from December 11 and the second dose by January 17 2022.
Interislander has also updated its refund policy. Anyone who wishes to cancel bookings because of their new COVID policy will receive a full refund, and there is no charge for people needing to move travel dates due to a COVID test.