The Capital Connection train service between Palmerston North and Wellington has lost more than $750,000 in the past 18 months and KiwiRail says it will drop the weekday link if it cannot stem the losses.
Documents obtained under the Official Information Act show the Capital Connection's monthly losses have climbed steadily since other commuter trains began travelling up to Waikanae more than a year ago.
The largest monthly loss was $84,275 in January and the deficit over the past year and a half totalled $759,590.
KiwiRail passenger general manager Deborah Hume says they had hoped patronage would pick up but this has not been the case, and if they cannot find a solution they will have to stop the service soon.
Wellington and Manawatu-Whanganui regional councils are willing to subsidise the service if the Transport Agency does the same, but the agency is declining to do so as it says the service does not relieve congestion.
Palmerston North MP Iain Lees-Galloway says it would be a huge blow for Palmerston North if KiwiRail cuts the service.
He says the Transport Agency could, and should, contribute, especially given the commuter service to the Wairarapa receives funding.
The Green Party says the Government and its transport officials need to realise that if the Capital Connection stops the result will be more traffic on the roads, which the agency says it's trying to relieve.
Transport Minister Gerry Brownlee says KiwiRail is well within its rights to examine the future of Palmerston North to Wellington service, as it can't afford the losses.
About 13,000 passengers a month use the Capital Connection. At present, it is the only commuter service which does not receive any form of subsidy.
KiwiRail says the service will continue to run until at least the end of next month.