In the UK, hundreds of thousands of rail passengers are facing the worst disruption since the 1990s.
Drivers are going on strike over changes to the roles of train staff and driver-only trains.
Commuters are being advised not to travel today, tomorrow or Friday.
The operator's owners Southern Railway lost a legal bid to halt the walkout, which will mean many commuters will have to work from home, take time off, or attempt to drive because of the huge disruption.
Members of the drivers' union will strike on Tuesday, Wednesday and Friday.
Charles Horton, chief executive of Southern's parent company Govia Thameslink Railway (GTR), confirmed there will be no services on strike days and "severe disruption" during an ongoing overtime ban.
The shutdown of Southern's services will be the worst disruption since the railways were hit by a lengthy strike by signal workers in the mid 1990s.
RMT drivers on Southern will also be on strike, while the guards will launch a fresh 48-hour walkout from next Monday, and a three-day stoppage from New Year's Eve.
GTR lost a legal bid in the High Court last week to stop the drivers' strikes, before also losing its appeal on Monday.
Around 300,000 passengers travel on 2,242 Southern services every weekday, including busy commuter routes from Sussex to London Victoria.