Rail union leaders fear job cuts announced by Thames Trains will lead to poorer station services for passengers in Oxfordshire.
The Transport and Salaried Staffs Association, which represents administrative staff workers, said the company's plans to reduce ticket office staff would lead to missed trains and unnecessary delays.
Thames Trains confirmed it was planning to make job cuts to keep costs under control.
It is attempting to run without a Government subsidy, which has been reduced from £34m a year to zero over the past seven years.
News of the job cuts follows plans to axe evening trains between Bicester and Oxford later this month.
Jo Twite, of the TSSA, said the job cuts would mean fewer ticket office staff on duty, leading to longer queues for passengers.
Thames Trains spokesman Jonathan Radley said the cuts would initially be met by not filling some job vacancies.
Changes in working practices were also being discussed.
He added: "There's no economic justification for running trains along the Oxford to Bicester line that are only used by eight people."
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