FRANKFURT, Germany (AP) — Lufthansa flight attendants walked off the job today at Germany’s busiest airport, causing more than 200 flights to be canceled as their union warned of more stoppages unless the airline gives in to its demands.

Lufthansa, Germany’s largest airline, said it canceled more than 200 shortand medium-haul flights from and to Frankfurt airport after some 1,000 cabin crew went on strike. A small number of long-haul flights were canceled as well, including to and from New York, Boston and Seattle.

Thousands of stranded passengers crowded Frankfurt’s main terminal building waiting for word on their flights. Lufthansa workers handed out water and juice to people stuck in long lines.

The short-term strike was to last eight hours until early afternoon, but Lufthansa said it would affect Frankfurt flight traffic throughout the day.

Airline spokesman Klaus Walther accused the UFO union of putting its demands “on the back of the customers” and urged them to return to the negotiation table.

But UFO union head Nicoley Baublies said on Bayerischer Rundfunk radio that the Frankfurt strike may just be the beginning if Lufthansa does not meet its demands. The union called the strike after 13 months of negotiations for higher pay and guarantees on conditions failed to produce an agreement.