(CNN) -- Belgian airspace was shut for 24 hours Tuesday afternoon because of a strike by Belgian air traffic controllers, officials said.
The two sides held one last meeting Tuesday but failed to avert the strike, which began at 2 p.m. (8 a.m. ET), said Guy Visele, a spokesman for Belgocontrol, the Belgian air navigation service provider.
"We do not even know what they want," Visele said, calling it a "wild action" by the unions.
The strike was not related to Europe-wide protests, scheduled for Wednesday, over government austerity measures, a Belgocontrol spokeswoman said earlier.
Britain's Foreign Office warned travelers to expect flight delays and cancellations and said domestic and international flights in Belgian airspace would be affected.