A one-day strike has been announced by members of the RMT union on the Southern rail network after talks to resolve a dispute failed.
The RMT had warned of further strikes after discussions ended on Tuesday without the union and rail operator reaching a deal.
Conductors will walk out for 24 hours on 22 February in the long-running row over guards' roles on trains.
Southern said it would run as many trains as possible during the strike.
Nick Brown, chief operating officer of parent firm Govia Thameslink (GTR), said: "We are disappointed that the RMT is going to heap yet further misery and disruption on the travelling public.
"We aim to run as full a service as we can."
He said during the last conductors' strike, which took place on 23 January, Southern ran about three-quarters of its normal service.
After talks broke down on Tuesday, the RMT said GTR was only prepared to discuss how to extend driver-only operation - the issue at the heart of the dispute.
The bitter row has centred on Southern's desire to turn guards into on-board supervisors. As such, they lose responsibility for opening and closing carriage doors, with that role falling to the drivers.
RMT general secretary Mick Cash said: "The abject failure by Southern rail in yesterday's talks to take the safety issues seriously has left us with no option but to confirm further action."
The union wants GTR to guarantee a second "safety-critical" member of staff on trains.
Aslef ballot result
Mr Cash said: "These disputes could have been settled if Southern had listened to our case."
He called on the rail operator to "engage in genuine and serious talks that address our issues".
GTR has been in dispute with two unions - the RMT which mostly represents conductors, and Aslef which represents drivers.
Aslef reached a deal with Southern on 2 February and has been balloting its members on whether to accept it, with the result expected on Thursday.
The deal includes details of circumstances when a train can be operated as driver-only, without an on-board supervisor.