The Auckland Ratepayers' Alliance claims switching to a public transport National Ticketing Solution will cost Auckland ratepayers at least $237.2 million.

Auckland Transport signed up to the system back in October, which will see the AT HOP Card replaced with a national card, as well as other added payment methods.

Using figures obtained under the Official Information Act, the alliance estimates the IT upgrade will cost Aucklanders $136.9-million, with ongoing costs of $100.3 over the next decade.

Spokesperson Josh Van Veen says the system is an unnecessary expenditure at a time when ratepayers can least afford it.

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