A series of strikes on Southern trains in the UK has begun as a long running dispute over the role of guards on-board.
Three days of industrial action began at midnight and is set to continue until Friday morning.
Southern said it expected to run nearly two thirds of its services over the period.
At the same time services between Brighton and Gatwick Airport are being disrupted because of over running engineering work by Network Rail.
Southern warned passengers may be delayed by up to 30 minutes and some trains would be cancelled or revised.
The RMT revealed it had received a legal challenge just hours before the start of the walkout.
The union said the strike would go ahead while it examined the details of the paperwork.
Another 11 days of action are planned before Christmas.