Rents at Auckland Airport have increased by up to 40 per cent in the past three years, and increased competition has made running a profitable business in the international terminal tough for some retailers.

But Auckland Airport is defending claims of "huge rent increases" for its tenants. It says the number of international travellers to New Zealand has increased by more than 37 per cent in the last five years, "creating opportunities for retailers".

It says its rents, set during a tender process, are comparable with similar Australian airports.

"Rental costs also reflect the opportunity retailers have for longer trading