Luxembourg - Controls on Schengen borders can be extended beyond six months because threats to public policy or internal security are not necessarily limited in time, an advocate general of the European Court of Justice says in his opinion regarding a case concerning border controls between Austria and Slovenia.

Advocate General Henrik Saugmandsgaard Oe also says this is subject to particularly strict criteria, so every time a Schengen zone member notifies the European Commission of its plan to extend border controls, the Commission must examine thoroughly whether all the strict conditions are met.

And "where reapplication has taken place several times in a row, as in the present case, the enhanced proportionality condition becomes even stricter each time".

The opinion is related to Austria's reintroducing border controls on the border with Slovenia ever since it introduced them amid the 2015 refugee crisis.

It comes after a court in Austria turned to the EU court for an explanation after a Slovenian citizen who refused to show his passport to Austrian authorities twice in 2019 and was fined EUR 36 turned to court to challenge the fine.

Although the advocate general's opinion is not binding, judges usually follow it.

Countries which are members of the passport-free Schengen zone, including Slovenia and Austria, have no border controls on internal Schengen borders in principle.

But due to the refugee crisis, several EU members, including Austria, Germany, Denmark and Sweden, reintroduced them, with some prolonging them ever since.