Pilots at Eurowings began a three-day strike on Monday, forcing the German airline to cancel hundreds of flights.
The strike action began at 00.01 a.m. local time (22.01GMT) and is set to continue until Wednesday 23.59 p.m. (2159GMT), according to a statement by the pilots' union Vereinigung Cockpit.
Lufthansa Group's low-cost airline has asked passengers to check the current status of their flight online before travelling to the airport.
"Eurowings deeply regrets the inconvenience caused to passengers and is doing everything possible to minimize the impact of the strike action on them," it said in a statement.
In the early hours of Monday, 185 flights to and from the Dusseldorf, Cologne-Bonn, and Stuttgart airports were canceled.
Domestic flights have been hit hardest by the pilots' strike, while the carrier said flights operated by Eurowings Europe and Eurowings Discover would not be affected by the strike.
The pilots' union decided last week to stage a three-day strike after talks with the Eurowings management failed to produce a deal on working conditions.
Vereinigung Cockpit is demanding a reduction of maximum working hours and longer rest periods, while Eurowings is insisting that the union's demands are not economically viable.
