Do Articles 18, 45, 49 and 56 of the Treaty on the Functioning of the European Union preclude provisions under which an employer established in one Member State is obliged to make advance payments of tax on the income of workers (nationals of another Member State) temporarily assigned to the employer by a temporary work agency established in another Member State through a branch established in the first Member State?
Do Articles 18, 45, 49 and 56 of the Treaty on the Functioning of the European Union preclude provisions under which the basis of assessment of such workers is set at a flat rate of at least 60% of the amount invoiced by the temporary work agency in cases where the intermediation fee is included in the amount invoiced?
If the answer to the first or second question is yes in the affirmative, is it possible, in a situation such as the present case, to restrict the said fundamental freedoms for reasons of public policy, public security or public health, or for the effectiveness of fiscal supervision?