Buses are set to replace trains in parts of the county as Southern Railway announced the implementation of a new emergency timetable.
Southern announced that from Tuesday until further notice, services between Lewes and Seaford are all cancelled.
Bus services will operate between Seaford, Bishopstone, Newhaven Harbour, Newhaven Town, Southease and Lewes.
It is not the first time passengers on the Seaford branch line has had its services axed. Around 80 per cent of trains on the route were axed in July.
Members of the Rail, Maritime and Transport union on Southern will strike for three days from Tuesday in protest at changes to the role of conductors.
The drivers’ union Aslef is due to start an overtime ban on Southern from Tuesday ahead of strikes later in the month and in the new year in a row over driver-only trains.
Southern is taking legal action to try to stop the strikes, but if the action goes ahead, services will be crippled.
Southern warned passengers to expect “severe and significant” disruption to Southern and Gatwick Express services every day from Tuesday.
Southern is advising that Aslef’s continuous drivers’ overtime ban will severely affect services every day.
On RMT strike days this will result in only around 50% of the full timetable being able to operate. If the Aslef strikes go ahead, no Southern services will operate, with only Thameslink services to Three Bridges and Brighton and a limited service on Gatwick Express.
Southern director Alex Foulds said: “Regrettably, because of this wholly unnecessary and unjustified industrial action, there will be severe and significant disruption on our network from Tuesday and customers are advised that stations will be incredibly busy.
“If passengers can make alternative travel arrangements they should, and if they don’t have to travel they shouldn’t. If the drivers’ strikes go ahead, there will be no services on Southern and customers should not attempt to travel.
“We’re doing everything we can to stop the drivers’ strike and that’s why we are seeking an injunction in the High Court.
“This industrial action is a clearly co-ordinated and cynical manoeuvre by the unions to bring yet further travel misery to passengers as well as having a detrimental impact on the regional economy when it least needs it.
“If the unions are listening to passengers then they will call off all industrial action now and give hardworking commuters and their families their lives back.”
Thameslink is not directly affected by the strike action, although its services are expected to be extremely busy.
Other operators’ services are not affected, but are likely to be busier.