Lufthansa canceled 140 flights Wednesday as pilots for the German airline launched their fourth strike in five months over pay for pilots hoping to retire early. The strike is expected to cost Lufthansa $2.5 million to $5 million in lost profit.

The Vereinigung Cockpit union, which represents Lufthansa pilots, said Tuesday that pilots were walking off the job from 10 a.m. to 6 p.m. local time in Munich, Germany. The airline typically runs 320 flights out of Munich, second only to Frankfurt, where the Vereinigung Cockpit held a strike last week. Lufthansa has not canceled any of their long-haul flights.

Lufthansa is rebooking passengers of canceled flights at other nearby European hubs and offering those traveling within Germany train vouchers with Deutsche Bahn. The strike affects both flights out of Munich and flights into Munich. See a list of canceled flights here.

A three-day strike in April cost Lufthansa $77 million. Lufthansa is reportedly working with pilots on a new early retirement package to avoid further strikes. Lufthansa now pays pilots a supplemental benefits package of up to 60 percent of their pay starting at 55 to last until the state pension system starts paying them. Lufthansa wants to raise that threshold from 55 to 60, in a bid to save money in the face of tough competition from budget airlines and growing Middle East and Gulf airlines

“We want to provide the pilots with a more concrete offer, which we will work on over the next few days,” Lufthansa Chief Executive Carsten Spohr said in Frankfurt on Tuesday. “This offer will be communicated at the start of next week.”

 “We believe we have the best pilots. They are an asset to be protected, but we have to make sure we can afford them,” Spohr continued.

Lufthansa shares have dropped 32 percent since June. Shares fell 1 percent Wednesday morning.