Flight cancellations at Hamburg Airport after a surprise strike by workers affected more than 40,000 passengers on Sunday, a day before a planned wider protest across Germany amid new contract negotiations.

The airport in Germany’s second largest city said the one-day strike, called over pay and conditions, began earlier than expected “without any notice.”

A one-day strike by workers at 13 German airports, including the Frankfurt and Munich hubs and all the country’s other main destinations, caused the cancelation of most flights on Monday.