Takanini passengers were slugged penalties on Thursday because both HOP card machines were out of order at the platform.

Auckland train commuters were over-charged due to a fault with HOP card machines, but Auckland Transport says it won't issue refunds unless passengers complain.

Commuters at Takanini train station on Wednesday found both tag-on machines on the platform were out of order.

Everyone who caught a train during the outage was charged a penalty fee when they hopped off because they hadn't tagged on.

Passenger Gareth Poley said he was fined even though he had a valid monthly pass.

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When he arrived at Newmarket station he said he went to the counter to tell them the HOP card machines were broken at Takanini.

He was told "you've been penalised, you should have bought a ticket".

The staff member said to him he had been charged a penalty fee for not tagging on, but he wasn't told how much it was for, just that it automatically came out of his credit card linked to his account.

"Had I not reported it to her they would have taken it off without me being aware of it," he said.

Poley said he intended to contest the charge because he was already paying $200 per month for the monthly pass.

Auckland Transport spokesman Mark Hannan said all passengers who hopped on at Takanini were charged $4.90.

"This will be more than the fare for some customers, the correct fare for others, and less than the correct fare for the remainder," he said in a statement.

"We don't proactively refund, because we don't know where the travel originated – i.e we don't know the customer tried to tag on at Takanini and that is why they have the missing tag off (or on).

"If customers can let us know then we will certainly look at a refund."

Hannan said having all units out of service on a platform at the same time was "rare".

Poley said he was concerned that many passengers who have a monthly pass would have been charged extra without realising.

Requests for refunds can be made through Auckland Transport's website.