Workers on South Western Railway are to strike for five days next month in the long running dispute over guards on trains.
Members of the Rail, Maritime and Transport union will walk out from June 18 to 22, the week of the Royal Ascot race meeting.
Ascot is served by SWR trains.
The company also serves London Waterloo, the busiest railway station in the country.
The union accused the company of "dragging its heels" on resolving the bitter guards row.
Talks had been protracted since industrial action was suspended in February, said the union.
RMT general secretary Mick Cash said: "Our members are angry and frustrated that, despite suspending action in good faith, and entering into talks in a positive and constructive manner, South Western Railway have dragged their heels and failed to bolt down an agreement that matches up top our expectations on the guard guarantee.
"For more than three months we have sought to negotiate a conclusion to this dispute and it is wholly down to the management side that the core issue of the safety-critical competencies and the role of the guard has not been signed off.
"It is because of that crucial failure by SWR that we have had no option but to lift the suspension and move back into strike action."
