Lufthansa blamed railway construction work for Wednesday’s IT meltdown after a telecommunications cable was severed, forcing it to ground flights and urge domestic passengers to travel by rail.

The carrier said the issue was fixed on Wednesday afternoon and that it was restoring normal operations, but it is now bracing for the impact of a strike by the ver.di civil service union.

Lufthansa has warned a large number of its flights could be affected by the action on Friday, which will take place at a number of major German airports including Frankfurt – the airport most severely affected by Wednesday’s outage – and as well as Munich, Hamburg and Hannover.

"For Friday 17 February, the trade union ver.di has called for a one-day strike at various airports in Germany," said Lufthansa. "As the airports of Frankfurt and Munich are also affected, a large number of Lufthansa and Lufthansa Group flights are expected to be affected."

Munich airport said "regular flight operations" would be suspended on Friday, while Frankfurt warned there would be "heavy disruption" throughout the day. "Passengers are strongly advised to refrain from travelling to the airport," it said in a statement, adding connecting flights from France would also be affected.