Security workers at Frankfurt airport went on strike on Friday, prompting dozens of flight cancellations and causing delays to travellers passing through Europe's third-largest hub.
Union Verdi had called on security staff employed by private firms grouped under the BDSW banner to strike from 0100 GMT until 2200 GMT in a bid to achieve higher pay.
That means far fewer staff at areas like security checks, leading to delays for passengers trying to board planes.
Airport operator Fraport, which is drafting in extra staff to help manage the queues, said around 41 flights had so far been cancelled and more could be expected.
Airline Lufthansa cancelled around 35 flights, mostly to destinations within Germany that can also be reached by train.
The union is calling for a hourly pay rate of 16 euros ($22.01) for security employees in the state of Hesse and said employers had offered between 10 euros and 13 euros an hour. Workers in other states get up to around 15 euros a hour, it said.
The BDSW has said it cannot meet Verdi's demands for immediate pay rises of up to 30 percent in some cases