A five-day strike on the Southern rail network has been announced by the RMT union in a long-running dispute over the role of guards.
Members have staged several walkouts, with the next action set for 8 August.
Parent firm Govia Thameslink (GTR) wants to use new trains where the driver operates the doors using CCTV, but the union fears job losses and has raised safety fears about the move.
GTR said it was unacceptable passengers were being made to suffer.
A spokesman for the Rail Delivery Group called on union leaders to end the dispute and said that drivers already open and close the doors on thousands of trains every day.
That had been deemed safe by rail safety experts and the independent regulator which oversees safety on the railway.