Case C-232/01 Politierechtbank te Mechelen – Belgium.
A worker is a citizen of Belgium and lives there. He works in Luxembourg and get use of a car (registered in Luxembourg) as part of their job, which he can also use personally.
Article 39 EC prevents Belgium from requiring that the car be registered and owned in Belgium. Doing so would discourage people from seeking work in other member states and discourage employers from hiring from other member states.
The decision applies to all EU member states