The airport authority said around 300 flights to and from one of Germany's busiest airports were canceled, affecting some 35,000 passengers.
Services sector trade union Verdi called a "warning strike" on Monday to demand a 10.5% raise in base wages, or at least 500 euros ($544) per month over a 12-month period.
The latest round of negotiations on Tuesday failed to properly address employees’ material and workload concerns, unionists said. The next round of talks is scheduled for February 22-23 and the follow-up for March 27-29.