Commuters in Sussex and Surrey could face train delays and cancellations after conductors on Southern railway decided to stage three 24-hour strikes.
These are part of a dispute over changes to their role and the introduction of driver-only trains.
Members of the RMT union will walk out at 11am on next Tuesday (26 April) and at the same time on 10 and 12 May.
The union is against plans for a new grade of on-board supervisor and proposals for drivers to operate doors.
A spokesman for Southern, which is run by Go Via Thameslink, described any possible strike action as “unnecessary and damaging” and said there would be no job losses or cuts in salary.
It urged the union to return to the negotiating table.