Network Rail has announced engineering work on Sunday, January 12, will mean no trains run between East Croydon and Gatwick Airport.
Passengers will have to rely on replacement buses.
The line closure will impact stations between South Croydon and Gatwick Airport, including Redhill.
Network Rail will use the closure to carry out maintenance at more than 50 worksites.
This includes track, signalling, and power supply system repairs, as well as clearing vegetation and litter.
Lucy McAuliffe, Sussex Route Director for Network Rail, said: “The lines between East Croydon and Gatwick Airport are among the busiest in the country.
“We don’t close them very often and when we do we look to make best use of that access to do as much work as possible to improve passenger journeys.”
Customers travelling between London and Gatwick Airport are advised to travel from London Victoria to East Grinstead, and then use rail replacement bus connections to the airport.
Rail replacement buses will also be available for local journeys, such as to and from Purley.
Jenny Saunders, Customer Service Director for Govia Thameslink Railway, said: “It means journeys will take longer, may involve a bus, and are likely to be busier than normal.”
