All of Lufthansa`s long- and medium-haul flights from Wednesday until Friday would be hit by the strike action, the trade union UFO said.
Lufthansa confirmed Tuesday that all of its flights from Germany would be affected from 4:00 a.m. (0300 GMT) Wednesday until midnight Friday.
Prior to the UFO`s extension of the strike, Lufthansa announced earlier in the day that it had launched legal action on Tuesday against its flight attendants in a bid to end their strike at Germany`s three main airports, namely Frankfurt, Munich and Dusseldorf, which are key hubs in Lufthansa`s network.
A Lufthansa spokesman said it was basing its case on demands by the UFO flight attendants` union being "too vague" and unjustified under the German labor law.
On Monday, Lufthansa had offered to raise the amount of a one-time payment to cabin crew members by 1,000 euros (1,075 dollars) to 3,000 euros and to back away from its proposal to raise its early retirement age from the current minimum age of 55 to 56.
The airline`s latest offer to resolve the industrial dispute was rejected by the UFO, which said it constituted only a "minimal" improvement.
The UFO wants to secure transition payments for its 19,000 members if they retire early, among other demands, as part of its contract dispute with Lufthansa, which is trying to cut costs.
Tens of thousands of passengers have been affected by hundreds of cancellations so far.
On Tuesday alone, Lufthansa was forced to cancel 136 flights, including 126 intercontinental flights and 10 European connections, the airline said.
Flights operated by Lufthansa subsidiaries such as Germanwings, Swiss and Austrian Airlines will not be affected.
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