Apron controllers, who guide planes in and out of parking slots, failed to reach a wage agreement with the airport operator, Euronews reported.
"The strike is about working hours, about breaks to recover, about shift systems, there are people who work seven days in a row with only two days off. We in this branch think that this is not responsible," said Markus Siebers, the traffic control union GdF's wages representative.
Airport operator Fraport said it is trying to operate at least half of its 1,300 daily takeoffs and landings during the strike, the Belfast (Ireland) Telegraph reported.
Operations at the airport should be back to normal Saturday, but may be disrupted again next week when more action is planned.
Ray Liotta sues skin care company over use of likeness
Aaron Carter is still in love with Hilary Duff