23. ←. The functional equivalent of extensions is legislation that makes agreements valid for all companies and workers (as in Iceland, Italy and Spain), but also, in a way, compulsory membership of an employers` organisation as in Austria. Employers seem to prefer multi-unionism in the workplace. This has often led to an agreement with trade unions on uniform rules for employee representation at company level, as in Italy. In some countries, such as the United States, the representation of a single union is established through a legal procedure.