Operations at a number of German airports are disrupted today as ground-handlers strike over pay.
Staff have walked out of airports including Frankfurt, Berlin, Stuttgart, Hanover, Duesseldorf and Cologne and are due to return to their posts by early afternoon.
German flag carrier Lufthansa says it has cancelled around 400 flights, mostly in and out of Frankfurt.
Public service workers' union Verdi called the strike after its demand for a 6.5% pay rise for its members was rejected. Employers countered with an offer of a 3.3% increase over two years.
Negotiations are due to continue on Wednesday and Thursday. Verdi head Frank Bsirske says he hopes today's strike will send "strong signals" to employers and encourage them to offer a more competitive pay rise.
However, German interior minister Hans-Peter Friedrich has reportedly dismissed the action as "disproportionate".
"Given that we have made a substantial offer, it is unjustified to mistreat the public with these strikes," he said, according to local media reports.
If the negotiations fail this week, the dispute could go to mediation.
Ground traffic controllers at Frankfurt Airport went on a series of strikes last month over a separate pay dispute.