Auckland Transport HOP card users may not know about a rule that renders top-up payments useless if not activated within two months.
But what some people do not realise, is that they are still entitled to that unused money.
Since May last year and April this year, up to $342,000 worth of transactions has been sitting with the transport agency, at some point.
The money is made up of transactions HOP card users have loaded on to their individual cards but have not activated by using the card within a 60-day period and therefore cancelling the balance.
Despite the 60-day rule included in Auckland Transport's terms and conditions page, some people have found themselves stuck after attempting to use a card that has not been active since they topped it up online months before.
AT spokesman James Ireland said the rule was put in place mainly to ensure that the tagging system used for travel on buses, trains and ferries around Auckland did not slow down by having to search for data or information on a card that was inactive.
"When you complete a transaction online, an action is added to the system which requires the HOP card to be tagged on before the action can be completed, which is when the balance is officially loaded onto the card.
"Several times a day the new actions get added to the list which is stores in every tagging machine. Tagging machines such as the posts at train stations are wired to the server. But for buses the data gets uploaded when the bus returns to the depot," he said.
"The main reason for the 60-day tag-on limit is to ensure the amount of data held does not cause the tagging system to slow down, as it has to search the database when each card is tagged on.
"Top ups done in a machine do not get added to the action list as the card is in the machine, completing the transaction."
Ireland said the $342,000 worth of transactions that had expired and sat with Auckland Transport since last May includes money that has been reinstated.
As part of the 60-day rule, people affected can still have their top-up money returned if a user contacts the transport agency.
The rule states there is no limit to the number of times - or the time since the top up was made - that an expired top up can be reactivated.
"It also includes situations where a HOP card is lost before the transaction has been completed and the money has been reinstated to the new card,'' Ireland said.
But Herald readers say the rule has caught them out and left them frustrated.
Sharon wrote: "I don't use the Hop card everyday but have it for when I can, I want to use public transport so I've been caught out by the 60 day rule.
"I travel a lot and have transport cards for London, Sydney , Melbourne and Singapore and I can use these cards when I am in the country with no fear that it won't work - even months / years later.
"Auckland transport seriously need to get with the times."
For more info visit: AT HOP card