Hungary’s decision to release foreigners convicted of human-trafficking triggered protests by its neighbour Austria on Monday with Vienna summoning the Hungarian ambassador.

Citing overcrowded prisons, Hungarian Prime Minister Viktor Orban’s government issued a decree in April allowing the release of foreign nationals convicted of people smuggling, on condition that they leave Hungary within 72 hours once freed.

“We think this is an entirely wrong signal,” Austrian Foreign Minister Alexander Schallenberg told journalists ahead of a European Union meeting in Brussels, adding that he demands “full clarification” from Budapest.

Austria is a prime destination for smuggled migrants heading for the heart of the EU via Hungary from the Balkans, and Vienna regards the release of human traffickers as a security threat.

For many migrants the Hungarian route remains an appealing one despite stepped-up border police patrols and a steel fence built by Hungary after the EU’s 2015 migration crisis.

Once in Hungary, migrants can move across generally open borders within Europe’s Schengen zone to wealthier EU countries like Austria or Germany.

In power since 2010, the nationalist Orban has pursued anti-immigration and tough asylum policies putting him in conflict with the EU and drawing criticism from the U.N. refugee agency.

Hungarian Foreign Minister Peter Szijjarto, addressing a news briefing on Monday, defended the release of prisoners on Monday, saying it was a “sovereign Hungarian decision”.

“We extradite foreign criminals and it is better they leave the country,” Szijjarto said after speaking with Schallenberg.

More than 13% of those in Hungarian jails have been incarcerated for human trafficking, National Prison Service spokesman György Makula told news site index.hu.

Hungarian police have turned back or detained more than 2,000 illegal migrants per week over the past month along the southern border with the Balkans region, according to police data.