In this case the Court ruled that Union law prohibits expulsion of a national of a Member State on general preventive grounds. Restrictive measures, such as expulsion, must be based on an actual threat and cannot be justified just by a general risk.
Expulsion can be ordered in the case of breaches of the peace and public security actually caused by the individual defendant himself/herself. Matters unrelated to the individual may not be taken into account. (full text)

This case concerned a worker who was involved in trade union activities.
The Court ruled that the right of a national of any Member State to enter the territory of another Member State, to stay there and to move within it, may not be restricted unless the presence or conduct of this national constitutes a genuine and sufficiently serious threat to public policy. (full text)

Exceptions to free movement of workers have to be based on public policy, public security and public health. However, these exceptions are not considered as conditions precedent to the acquisition of the right of entry and residence. They provide for the possibility, in individual cases where there is sufficient justification, of imposing restrictions on the exercise of a right.
The granting of a permit is a measure of a Member State that serves to prove the individual position of a national of another Member State. The failure of a national of a Member State to complete the legal formalities on access, movement and residence does not justify a decision that orders expulsion based on a breach of public policy or public security.

The existence of a previous criminal conviction can only be taken into account with regard to expulsion of a national of another Member State in so far as the circumstances which gave rise to that conviction are evidence of personal conduct constituting a present threat to the public policy. The existence of such a threat implies the existence in the individual concerned of a tendency to act in the same way in the future. It is possible that past behaviour alone may constitute such a threat.
The concept of public policy has to be interpreted strictly so that its scope cannot be determined unilaterally by each Member State. However, particular circumstances justifying recourse to this concept may vary from Member State to Member State and from one period to another. Therefore, competent national authorities have an area of discretion, within the limits imposed by the Treaty and the provisions adopted for its implementation. (full text)

The Court confirmed that the freedom of movement can be restricted on grounds of public policy, public security and public health. Further, the Court held that a residence document has only a declaratory effect.
In this case the Court held expulsion incompatible with Union law. National authorities are not entitled to impose penalties which are so disproportionate to the gravity of the infringement (non-compliance with administrative formalities) that they become obstacles to the free movement of persons. Imprisonment was not proportionate in this situation. (full text)

The Court ruled that a Member State may not expel a national of another Member State from its territory or refuse him/her access to its territory by reason of behaviour which, when caused by the State’s own nationals, does not give rise to repressive measures or other genuine and effective measures intended to combat such behaviour. Circumstances not related to the specific case, in respect of citizens of Member States as justification for measures intended to safeguard public policy and public security, may not be relied upon.
The notification of the grounds justifying expulsion or refusal of a residence permit must be sufficiently detailed and precise. This will enable the person concerned to defend his/her interests. (full text)

In this case the Court ruled that Member States may take administrative police measuresagainst migrant workers if
- such action is justified by reasons of public order or public security based on his/her individual conduct;
-by reason of their seriousness, those reasons could otherwise give rise only to a measure prohibiting him/her from residing in, or banishing him/her from, the whole of the national territory;
- the conduct which the Member State concerned wishes to prevent gives rise, in the case of its own nationals, to punitive measures or other genuine and effective measures designed to combat it.
If these requirements are met, the measures will not be regarded as discriminatory. (full text)

The expulsion of nationals of other Member States is an obstacle to the freedom of movement for workers. In this case the Court held that such an obstacle may be justified on grounds of public policy, based on the personal conduct of the individual concerned. Previous criminal convictions are not in themselves sufficient to justify an obstacle. The concept of public policy presupposes a genuine and sufficiently serious threat which affects one of the fundamental interests of society. The national authorities have to consider in every case whether the personal conduct constitutes a present threat of public policy at the time of the expulsion.
This examination has to be made in compliance with the general principles of Union law. Special attention has to be paid to the fundamental rights, especially the right to family life. (full text)