Mr Froggatt said the union asked Auckland Transport for hand-outs to give passengers travelling for free with their SuperGold cards two months ago but only limited informational brochures had been provided.
He believed the advertising process had been left too late and that it would take up to three months to capture the majority of those who travel on the scheme.
Mr Froggatt also questioned what would happen to pensioners outside Auckland who travelled to the city.
Auckland Transport spokesman Mark Hannan said their relationship was with the bus companies and not the drivers directly, and the council body has not issued any instructions to companies on how to deal with their employees.
From July 1, customers without an AT Hop SuperGold concession will be handed an information leaflet telling them about the change to SuperGold and advising them what the process is to get the concession loaded.
Mr Hannan said it has asked operators to show discretion after the deadline.
NZ Bus northern chief operating officer Shane McMahon wasn't able to comment.
For the last two months, Auckland Transport has been moving SuperGold cardholders on to AT Hop cards with a concession loaded so they can continue to have free public transport.
Seniors need to buy a $10 AT Hop card with a minimum of $5 credit loaded on to it by July 1 but Auckland Transport has conceded there will be a grace period until the end of the month.
Any senior citizens with a blue AT Hop card already loaded with a SuperGold concession would still be accepted after July 1.
A SuperGold card allows senior citizens to travel on public transport free of charge any time after 9am weekdays and all day on weekends and public holidays.