A VZW is an organisation of persons (natural or legal entities) that are bundling their professional knowledge, their activities, and their resources towards an objective that is not in pursuit of making monetary gains.  A VZW is not an industrial or commercial enterprise and is not aimed at garnering profits for its members. 
It may engage in an additional commercial activity if the latter is undertaken voluntarily and is not the collective object of the members.

Customarily, VZWs are liable to tax on legal persons. Nonetheless, certain VZWs are liable for corporate tax. As they are, by their very nature, not real companies, they are not subject to company contributions. 
Mandated officers of VZWs may, in contrast, become obligated in certain instances to affiliate with a social insurance fund.