Southern train guards walked out on Tuesday, causing massive disruption on the new Govia Thameslink Railway (GTR) franchise covering London and the south east.
The workers are fighting the introduction of driver only operation (DOO), which will remove safety critical duties from the guards and leave sole responsibility with drivers.
The guards are in the RMT union. Drivers’ union Aslef also opposes DOO.
Aslef is balloting for strikes against the introduction of 12-car trains on the Gatwick Express.
Bosses got a court order against drivers refusing to drive them.
GTR bosses threatened to dock strikers’ pay but failed to undermine the action.
The GTR franchise is the largest in Britain. Bosses want to make sure more tickets are sold at full price, changing the guards’ duties and penalising passengers to fill their own pockets.
Further strikes are set for 10 and 12 May.