The practice seems to be on a decline, according to this recent piece in The Economist:. For instance:
…the unions are continuing to lose members, as the older industries where they are entrenched trim jobs. Newer companies, especially in areas such as e-commerce, security firms and fitness studios, are “almost entirely without collective representation”, says Martin Behrens at the Hans Böckler Stiftung, a union-linked think-tank.
Workers at any German company with five or more employees can demand the creation of a works council. But in 2011 only 12.5% of all companies had one, down from 13.4% the year before. Only 659 German firms had supervisory boards with worker representatives in 2011, compared with 708 in 2007. Ironically, as America’s carmaking union seeks to bring Germany’s labour-market model into Volkswagen’s factory in Tennessee (see article), its future seems increasingly in doubt back home.
Here is a recent NYT piece on how Amazon’s labor practices clash with German union traditions.