Most of Lufthansa's, Germany's national airline, domestic, European and long-haul flights have been cancelled due to strikes by ground personnel and cabin crews.
"Due to strike action announced for April 22, nearly all Lufthansa flights to German and European destinations must be cancelled," the airline announced in a statement.
The firm said it had scheduled only around 20 of its usual 1,650 short-haul flights for Monday, and warned that long-haul routes would also be seriously affected.
At Frankfurt airport, Europe's third-busiest hub, 46 out of 50 intercontinental flights would be scrapped, with long-haul flights from Munich also grounded.
Services union Verdi called the strike after three rounds of pay talks with management ended without agreement.
Verdi is demanding a 5.2 percent pay increase for 33,000 Lufthansa ground staff, plus employees of various subsidiaries, as well as cabin crew members who are Verdi members.
The escalating pay dispute threatens to cause transport chaos across Germany, Europe's largest economy.
It comes a month after Lufthansa cancelled nearly 700 out of a total 1,800 flights due to half a day of warning strikes.
Lufthansa board member Stefan Lauer said the action, described as a 24-hour warning strike, was "de facto an all-out strike" that was "a completely excessive measure that can in no way be justified in view of the current state of negotiations".
Verdi has accused management of "playing with employees' fears about their future and their jobs" in refusing to make any concrete guarantees.
The union has complained that the offer proposed by management represented an increase of less than one percent over a period of one year.