Key facts of the case:

Reference for a preliminary ruling — European Union Citizenship — Articles 18 and 21 TFEU — Request to a Member State by a third country seeking extradition of an EU citizen who is a national of another Member State and who has exercised his right to free movement in the first Member State — Request made for the purpose of enforcing a custodial sentence and not for the purpose of prosecution — Prohibition on extradition applied only to own nationals — Restriction on free movement — Justification based on the prevention of impunity — Proportionality.

Outcome of the case:

In those circumstances, the Korkein oikeus (Supreme Court) decided to stay the proceedings and to refer the following questions to the Court for a preliminary ruling:

‘(1) Are national provisions on extradition to be assessed with respect to the freedom of movement of nationals of another Member State in the same way regardless of whether the extradition request of a third State on the basis of an extradition convention concerns the enforcement of a custodial sentence or a prosecution as in the case giving rise to the judgment of 6 September 2016, Petruhhin (C‑182/15, EU:C:2016:630)? Is it relevant that the person who is the subject of the extradition request, as well as being a citizen of the Union, is a national of the State which has made that request?

(2) Does a national law [of a Member State] under which only its own nationals are not extradited outside the EU for the enforcement of a penalty unjustifiably disadvantage nationals of another Member State? Are the mechanisms of EU law by means of which an objective, acceptable as such, may be achieved in a less prejudicial manner applicable also in an enforcement situation? How is a request for extradition to be answered in a situation in which, such mechanisms being applied, the request is notified to another Member State which, however, does not, for example because of legal obstacles, adopt measures concerning its nationals?’