Wellington's officials are worried the older planes used by Singapore Airlines on its flights into the capital from Singapore are reducing the route's value.
The council is subsidising flights from Singapore to Canberra and on to Wellington by about $8 million over the next decade.
Officials in Wellington and Canberra are concerned the age of the aircraft and level of service make it less competitive than flights out of Auckland.
In a report prepared by Wellington City Council, which the mayor Justin Lester will present on Thursday, officers said "the Singapore Airlines product could and should be improved".
"Specifically, that while the service is welcome in both cities, officials have some concern that the age of the aircraft and level of service may detract from the benefits of the service generally," the report said.
"Officials understand that due to the age of aircraft, the carriage volume may be limiting and that to be competitive with other airports, a more modern aircraft could and should be investigated for the route."
The report noted VisitCanberra executive director Ian Hill said that officials in Canberra also shared some of the same concerns.
Mr Lester disagreed with the report's assessment, and said it used language that did not fairly reflect the conversation that took place.
"I was there, so I was part of these discussions," he said. "It's the best service out of Wellington."
"Any improvement would be around getting that service from four days a week to seven days a week, and then ultimately getting a new plane as well because the current plane isn't the newest," Mr Lester said.
"But that's a programme of continual upgrades ... so if we want the best possible service, that's what we'll get from a new plane."
The report said passenger volumes between Wellington and Canberra were within the range expected, but Mr Lester could not provide specific details.
The Boeing 777-200 aircraft are the oldest in Singapore Airlines' fleet, and are 14.6 years old on average (the global average is about 13 years), according to planespotters.net.