The owners of Southern Railway have lost their High Court bid to halt a series of crippling strikes by train drivers.
Members of Aslef are due to walk out for three days next week and six days in January in a dispute over driver-only trains, which will halt all Southern services and affect hundreds of thousands of passengers.
French-owned Govia Thameslink Railway (GTR) argued that the action, which is lawful under English domestic law, would unlawfully restrict freedom of movement provisions under EU law.
But on Thursday, judge Sir Michael Burton refused to grant an injunction blocking what GTR called "unprecedented" strike action.
A spokesman for Southern said: "Naturally we're disappointed with today's decision. We will now immediately review matters with our legal team."
The judge granted GTR permission to appeal.