Lufthansa has canceled 140 flights after pilots walked off the job at Munich airport — their fourth strike in five months in a dispute that has cost Germany's largest airline tens of millions of euros (dollars).

The dpa news agency reports that Lufthansa says Wednesday's eight-hour strike by the Vereinigung Cockpit union at Germany's second-busiest airport affected some 15,300 passengers.

A three-day strike in April already cost the airline 60 million euros and Lufthansa says this stoppage will cost millions more.

The two sides are locked in a dispute over the pilots' demand that Lufthansa keep paying a transition payment for those wanting to retire early. The airline, which faces tough competition from European budget airlines and major Gulf airlines, wants to cut those payments.