Jetstar's decision to call time on its regional routes could force up the price of flights, Consumer New Zealand says.
The low-cost Australian airline, a subsidiary of Qantas, confirmed on Wednesday it is withdrawing services from Nelson, New Plymouth, Napier and Palmerston North from the end of November.
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That leaves most of the routes with only one provider - Air New Zealand.
Consumer New Zealand's Jessica Wilson told Newshub having a monopoly in place often doesn't end well for customers.
"It really is a question of putting more scrutiny on the airlines' prices, with any monopoly provider there's that real risk that consumers could end up paying more."
Wilson said Air New Zealand won't have as much pressure to give people a good deal with its main operation gone.
"The airline's decision to pull out of these routes will leave the market pretty much to Air New Zealand and with no major rival there won't be the same competitive pressures on price.
"That increases the chances that consumers will end up paying more."
Air New Zealand has already offered cheaper airfares to passengers who booked with Jetstar and will be affected by the changes.
Jetstar said it simply couldn't keep running the routes after giving operating in the regions a "real go".
"This decision is based on our regional operations continuing to be loss-making, combined with higher costs and a softening of the regional travel market," CEO Gareth Evans said.