Such barriers can arise not only from regulatory or administrative action by Member States but also from self-regulation, or the practices of professional bodies. They may include, for example, complex, lengthy and burdensome authorisation procedures, highly detailed and divergent rules on advertising, or administrative formalities imposed before companies can "post" workers (bring in their staff to work temporarily outside their own Member State of residence).
Elles peuvent inclure, par exemple, des procédures d'autorisation complexes, pesantes et interminables, des règles tatillonnes et divergentes en matière de publicité ou des formalités administratives à remplir avant que les entreprises puissent «détacher» des travailleurs (les envoyer travailler temporairement en dehors de leur propre État membre de résidence).