No Southern, Great Northern or Thameslink trains will run on "virtually all" routes this Friday (September 1).
Govia Thameslink Railway has confirmed that the disruption has been caused by industrial action by the ASLEF union.
A "very limited" shuttle service will run between London Victoria and Gatwick Airport.
The service provider warned that these trains will be extremely busy and will not stop at any other stations.
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On Saturday (September 2), a strike by RMT and an ASLEF overtime ban will mean that services will be limited across the Govia Thameslink network.
The first trains of the day will depart later, and the later services will finish earlier than usual.
According to Govia Thameslink Railway, passengers should expect longer waiting times and busier trains.
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On Sunday (September 3), trains before 9am will be subject to delays or cancellations because of the strikes.
Jenny Saunders, Govia Thameslink Railway's customer service director, said: “We're really sorry for the inconvenience this industrial action is causing to our customers.
"Please plan all your journeys carefully in advance, and check again before you set off.
"We strongly advise you to make sure you know the times of your last trains – including any connections – to make sure you can get home before services finish.”
Journeys can be checked via the National Rail website: www.nationalrail.co.uk
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