Germany's largest airline Lufthansa (LHAG.DE) said it was cancelling almost 1700 flights on Monday, mostly on domestic and short-haul European routes, as a result of planned strike action by thousands of workers calling for higher pay.
Verdi, representing 33,000 staff at the airline, announced the strike action on Friday to put pressure on Lufthansa management to make a better pay offer.
The union said the offer put forward by Lufthansa on Wednesday was "scandalous."
As with previous strikes, Lufthansa canceled mainly short-haul flights in order to keep more profitable long-haul flights in the air.
Lufthansa has estimated the strike will cost it tens of millions of euros and has described the labor action "absurd" and "out of proportion", given the early stage of negotiations.
"Despite an offer being made by Lufthansa in the last round of negotiations, despite constructive talks and further dates for more talks, Verdi is once again holding our customers hostage in this pay dispute," said Stefan Lauer on Friday.
Lauer is Lufthansa's executive board member for personnel and is leading the pay talks, although he is stepping down by the end of June.
Lufthansa's offer was to raise salaries by 1.2 percent from October this year and a further 0.5 percent a year later, in a deal that would run for 29 months and would not contain job guarantees.
Verdi wants a 5.2 percent pay rise for cabin crew and ground staff at Lufthansa Cargo, Lufthansa Technik, Lufthansa Systems, catering unit LSG Sky Chefs and ground crews. It is also seeking a commitment by Lufthansa to safeguard jobs.
Staff represented by Verdi have already held a one-day strike on March 21, forcing Lufthansa to cancel nearly 40 percent of its average 1,750 flights for the day.
Lufthansa also recommended passengers restrict themselves to hand baggage where possible, in an attempt to avoid the sort of queues seen at check-in desks in Frankfurt during March's strike.
Passengers with tickets for flights within Germany will be able to travel on the Deutsche Bahn train network instead.