South West Trains services along the Sussex coast will not run today because of a 24-hour stoppage by the RMT union.
The six trains a day that normally run between Reading and Brighton, stopping at stations in Sussex, will be cancelled.
There may also be disruption on Friday morning as services get back to normal.
The RMT has called the stoppage in a long-running dispute over issues including the wearing of red-coloured waistcoats.
SWT said it had offered to resolve all the outstanding issues but were rebuffed by the union.
The RMT had claimed talks had broken down following a series of rows, including the objection to wearing the waistcoats and name badges.
The RMT has announced a second strike for May 11.
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