Sunday morning services from Hastings to London are being scrapped.
Three trains departing at 6am, 7am and 8am will temporarily disappear this winter to allow extra engineering work to take place on the line on Saturday evenings.
The move by Connex South Eastern comes as the company axes 40 other services to help remaining trains run more punctually.
Managing director Michael Holden said: "We realise no one likes to see fewer trains but the new timetable allows more breathing space for us to improve performance and punctuality."
A spokeswoman for Connex said the majority of routes being scrapped would run in and around London and not affect commuters in Sussex.
She added the South East England Development Agency (Seeda) had funded three new services between Hastings and Charing Cross, which will start in the new winter timetable.
The timetable comes into affect on September 28 and the Sunday morning services could be reintroduced next summer.
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