Originair says it's already had to reduce flights between Westport and Wellington - and the route's now set to be axed by May.
The regional carrier stepped in when Sounds Air withdrew from the service in 2024.
Now, it says it's struggling with the small market and increasing operating costs.
Managing director Robert Inglis says it's cut the service back to three times a week - which went well over summer.
"But winter's another thing, and then, of course, the additional doubling of fuel price - we've just unfortunately had to make a hard call."
Originair has applied for Government funding to help it continue the service.
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