A court of appeal has ordered pilots at the German flag carrier, Lufthansa, to stop their strike, declaring the industrial action illegal.

The regional court of labor in the central German city of Frankfurt issued the injunction on Wednesday, describing the walkout as “unlawful.”

The court argued that the industrial action was no aimed at achieving a concrete goal with regard to wages, but rather against Lufthansa's plans to increase its budget airline subsidiaries.

German law does not allow strikes that take target company policy without concrete pay or benefits goals.

The fresh ruling overturned a Tuesday verdict by the Frankfurt state court, which had declined Lufthansa’s request for an injunction.

On Tuesday, Germany’s pilot union, Vereinigung Cockpit, began its action on long-haul flights, resulting in the cancellation of 90 flights.

The union also extended its walkout to medium- and short-haul flights on Wednesday. Lufthansa said 1,000 flights were cancelled while 140,000 passengers were grounded on the second day of the pilots’ strike.

Since April 2014, Lufthansa pilots have walked out of their jobs several times over pay, retirement benefits and the airline’s plans to expand low-cost operations.

The industrial actions have reportedly cost the German flag carrier over 300 million euros (338.4 million dollars).