In what is becoming an increasingly acrimonious labour dispute, nearly 800 short- and medium-haul Lufthansa flights were cancelled Friday, including 90 related to an Italian air traffic controllers' strike. Since the strikes began Wednesday, Lufthansa said some 180,000 passengers have been affected.
Lufthansa has been trying to find savings in the face of stiff competition from European budget airlines like Ryanair and EasyJet and major Gulf airlines like Emirates, Etihad and Qatar Airways.
The German government, alongside France, is also pressing the European Union to demand a fair playing field with the Gulf airlines, which are accused of receiving billions in states subsidies.
Lufthansa operates lower-cost carriers Germanwings and Eurowings, and announced it will add budget long-haul services at the end of the year in collaboration with SunExpress, a joint venture with Turkish Airlines.
The current dispute with the Vereinigung Cockpit union centres on a plan to cut transition payments for pilots seeking early retirement. The union has hit various Lufthansa units with around a dozen short-term walkouts over recent months.
Speaking in Washington earlier this week, Lufthansa CEO Carsten Spohr suggested the airline was set in its course.
"We are standing up to what we believe is right for the future sustainability of Lufthansa," Spohr said. "We have to do whatever it takes to create that future sustainability."
Lufthansa said in a statement after the strike extension that it had already presented a better offer to the union this month but that it had been rejected.
"With the notice of a fourth strike in just one week, the pilots have not only escalated the labour dispute too far, they have removed themselves even farther from a solution," the company said.
Vereinigung Cockpit accused Lufthansa of intransigence, but said a return to the negotiating table was possible anytime.
"But this would require Lufthansa to demonstrate a serious will to reach an agreement," spokeswoman Ilona Ritter said.