Hundreds of airline flights are grounded across Europe as cabin crews working for Lufthansa went on strike Friday.

Flight attendants walked off the job at midnight, part of an ongoing dispute with the German carrier over pay and outsourcing of jobs.

Lufthansa canceled some 1,200 flights in advance of the 24-hour strike and took out newspaper ads on Thursday, apologizing to customers. The company criticized workers, saying the strike is “disproportionate.”

The dispute between Lufthansa and the union representing about 12,000 of the airline's employees caused several smaller work stoppages earlier this week.

The strike has affected flights to and from Frankfurt, London, Paris, Moscow, Istanbul and Boston.

A statement on Lufthansa's website says the airline will do its “utmost best to minimize the impact on its customers.”

The company is offering customers traveling within Germany train vouchers for Deutsche Bahn in exchange for their plane tickets.