Germany's air transport network has been severely disrupted by a national strike, halting one-third of flights from Frankfurt airport on Tuesday.
The strike by baggage handlers and ground staff affiliated with the Vereinte Dienstleistungsgewerkschaft (Ver.di) union has also led national carrier Lufthansa to cancel hundreds of flights at Germany's largest airports.
Flight traffic is likely to be considerably affected and include cancellations, said a spokesman for Frankfurt airport operator Fraport.
On Tuesday Lufthansa cancelled 400 flights out of its usual daily schedule of 1,850 flights.
Air Berlin has also canceled eight flights, Reuters said.
As well as Frankfurt, the Munich airport would also be affected from 0400 to 1200 GMT, Dusseldorf from 0600 to 1200 GMT, Cologne from 0200 to 1000 GMT and Stuttgart from 0400 to 0900 GMT.
Ver.di has called on its workers to strike for a 6.5 percent pay increase and better conditions for trainees.
According to the Wall Street Journal, the union is demanding a minimum €200 a month salary increase for workers.
And if Tuesday's disputes fail to move state and local employers to raise salaries, Ver.di has warned of more widespread action in the coming weeks.
The chances are 50-50 for a full-scale strike, Ver.di spokesman Frank Bsirske told Reuters.
The latest strike follows action in February by fellow union GdF.
The GdF action also led to the cancellation of around 1700 Lufthansa flights, the WSJ reported, costing Fraport €4 million.
If talks between employers and the union fail to reach a conclusion this week, then the dispute could move to a mediation stage.
If this fails, Ver.di could then ballot its members for a more disruptive strike in April.