The majority of retired public transport users in Auckland have taken up the city's travel smartcard ahead of the switch becoming compulsory.
From July 1, those currently using their SuperGold cards in Auckland - which give seniors discounts and concessions including free transport in off-peak hours - will also need to buy a HOP smartcard to keep receiving travel perks.
The Auckland cards cost $10 and also require an additional minimum credit of $5.
In May, Auckland Transport launched a new campaign to get more SuperGold card users to take up smartcards.
About 90,000 SuperGold cardholders use public transport, and of those 71,428 have purchased HOP cards, Auckland Transport says.
Spokesman Peter Paton says all SuperGold cardholders will receive a letter this week reminding them of the need to switch.
New Zealand First leader Winston Peters previously called for the move to be dropped, saying Auckland seniors were facing chaos amid confusion about the switch.