Lufthansa said in a statement that it had grounded 74 out of a total 160 inter-continental flights scheduled tomorrow, affecting an estimated 20,000 passengers.
And around 60 per cent of Lufthansa Cargo flights would also be hit.
Originally, the pilots' union Vereinigung Cockpit had initially called for a 24-hour walkout on Wednesday, but subsequently extended the industrial action over four days.
The stoppages Wednesday had targeted short- and medium-haul services.
Long-haul and cargo flights were grounded yesterday and then short- and medium-haul flights again today.
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It is the 12th -- and now longest -- stoppage since the pilots began their industrial action last April.
The dispute hinges on plans by Lufthansa to scrap an arrangement under which pilots can retire at 55 and receive up to 60 per cent of their pay until they reach the statutory retirement age of 65.
Pilots are also concerned about Lufthansa's aim to further develop its low-cost activities as it faces growing competition.