Die HOAI. Until 2019, German law set both minimum and maximum fees for architects and engineers. Charging below the minimum was not permitted. The justification, stated by the professional chambers, was that binding rates protect planners and clients from ruinous price competition that would endanger quality and safety.
The European Court of Justice struck the binding rates down on 4 July 2019, holding that they obstructed price competition contrary to the Services Directive. Germany had to be told by a foreign court that price is something to compete on.