German airline Lufthansa has cancelled over 1,500 flights because its pilots union announced on Monday they would extend the 35-hour strike to include long-haul fleets.
The strike started at 1:00 a.m. local time on Monday (2300 GMT Sunday) and was planned to last until 11:59 p.m. Tuesday.
The union Vereinigung Cockpit (VC), which represents around 5,400 Lufthansa pilots, announced on Monday that the nationwide walkout would extend to long-haul routes and would affect all flights on Airbus A380, A340, A330 and Boeing 747 aircraft.
Initially, the union only called on pilots flying short and medium-haul flights to temporarily stop working.
According to Lufthansa's website, Europe's second largest airline had cancelled 1,564 flights by late Monday afternoon.
Lufthansa said its customers could cancel or re-book tickets free of charge. Passengers could also exchange flight tickets for train tickets where possible.
Flights operated by the Lufthansa's subsidiaries - Austrian Airlines, Brussels Airlines, Germanwings, SWISS and Air Dolomiti - would not be affected and would operate as scheduled, it said.
The two sides are in a dispute over pilots' retirement benefits. VC is asking Lufthansa to retain a scheme that allows pilots to retire early at age 55 while receiving 60 percent of their salaries.
Lufthansa planned to raise the early retirement age to 60 as a cost-saving measure.
"Unfortunately, Lufthansa has not taken up the compromise proposals of the VC after seven strikes since April this year and continues to stonewall," said the union in a statement on Monday.
Meanwhile, Lufthansa criticized the strike as "totally incomprehensible and disproportionate," insisting that its retirement benefits were "among the best (if not the best) in the world."
"The company also feels that the continuing series of strikes here only confirms that urgent action is needed to review the current strike laws in Germany for companies providing critical infrastructural facilities," the Lufthansa statement said.
The pilots' strike came just hours after German railway traffic resumed order after a 50-hour train driver walkout, which left millions of passengers stranded as school holidays were beginning or ending in nearly half of Germany's 16 federal states.
Train drivers were asking for five percent higher payment and a shorter work week by two hours from German state-owned railway company Deutsche Bahn. Their union said there would be a one-week break before any further strikes.
Germany is scheduled to enact a law in November to prevent small groups of employees from paralyzing the country's infrastructure by striking.