The Dutch term 'koepel' is often used to refer to some kind of 'umbrella organisation' (NL koepelorganisatie). More context information is needed though in order to decide whether this would fit in your specifc context.

This major project is an initiative of private parties who have bundled their forces in ‘Koepel windenergie Noordoostpolder’ (umbrella organisation wind energy north-east polder).
http://www.aegean.gr/environment/energy/mcda/Frames/NC2/Step...

http://www.riwa-maas.org/nc/en/riwa-meuse/organisational-str...