Southern Railway has advised passengers not to travel tomorrow, irrespective of the outcome of today's Court of Appeal case aimed at stopping a drivers' strike.
The train company added it will not be able to provide alternative travel, including replacement bus services, on the dates of the drivers’ strikes - due to take place on Tuesday 13 and Wednesday 14 December.
Further strikes are planned for Friday 16th, and from Monday 9th to Saturday 14th January 2017, according to the operator's website.
Conductors strikes are also due to take place between Monday 19th and Tuesday 20th December, and between New Year's Eve and Monday 2 January, causing further severe disruption.
The majority of Southern Rail's services will be affected by the strikes. A significantly reduced service will run between Brighton and London Bridge, and between Gatwick and London Victoria.
The company said commuters were "strongly advised to consider alternatives methods of transport wherever possible". The strikes will halt all Southern Rail's services, disrupting the 500,000 passengers who use the service every day.
Members of the RMT and Aslef unions have backed action in a dispute over driver-only operated trains. Southern Rail is in the process of appealing after a failed court bid to stop the strikes.
Angie Doll, passenger services director for Southern, said: "We hope for the sake of our passengers our application to the Court of Appeal is successful. Even if we are able to stop the strikes through the court, services will still be very heavily impacted tomorrow.
"We will work through the night to try and provide as many services as possible, but we are still advising passengers not to travel as we will not be able to offer a robust service they can rely on.
"We are sorry but the industrial action by Aslef leaves us no viable alternative, but be assured we will do all we can overnight."
Govia Thameslink Railway, the owners of Southern, lost a bid in the high court last Thursday to obtain an injunction to stop the action from going ahead.
Meanwhile union leaders have accused Southern of "deliberately sabotaging" train services - blaming the disruption on staff shortages, when drivers and guards were available to work.
The rail regulator is being urged to investigate claims the train company cancelled trains, in order to facilitate their court case against drivers on strike.
A spokesperson for Southern dismissed the claims as "fabricated nonsense" and said the company was "providing the best possible service under very challenging circumstances".
Home Secretary Amber Rudd meanwhile hit out at “this miserable period” of rail strikes that are set to cause Christmas chaos, calling the action "totally unacceptable".
Additional reporting by Press Association
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