Have a look at the Eurocontrol site
Eurocontrol Maastricht UAC - About Us
To quote (with my bold type edit):
EUROCONTROL's Maastricht Upper Area Control Centre (UAC) ensures the safe, efficient and expeditious flow of civil aircraft in the upper airspace (above 24,500 feet, or roughly 7.5 km) of Belgium, the Netherlands, Luxembourg and the North-West of Germany.