The new flight cancellations in and out of Germany's biggest airport, Frankfurt, as well as hubs in Munich and Duesseldorf, come after four days of stoppages that had already forced the airline to cancel 2,800 flights, leaving 300,000 passengers stranded.
The industrial action over a dispute with the UFO flight attendants union regarding cost cuts began on Friday with a pause on Sunday, and is set to go on until Friday.
The court dismissed the airline's argument that the union's reasons for striking were "too vague" and unjustified under German labour law.
The UFO union welcomed the ruling on its website, calling for the strike to continue from until Friday across all flights at Frankfurt, Munich and Duesseldorf airports.
Also Read
Lufthansa in a statement said it stood by its position that "the reasons for the strike were not defined clearly enough" and said it will decide its "next steps" today.
The same court is due to issue today a ruling for the remaining period of the strike.
The airline has been locked in a battle that erupted nearly two years ago with cabin crew over early retirement provisions which the union wants unchanged.
But Lufthansa argues that the system is too expensive in the face of cut-throat competition from low-cost operators such as Ryanair and Easyjet.
This is the first time that cabin staff have staged walkouts in the long-running dispute, which does not affect Lufthansa's subsidiaries Germanwings, Eurowings, Lufthansa CityLine, SWISS, Austrian Airlines, Air Dolomiti and Brussels Airlines.