Hungary has in recent weeks freed 777 foreigners, mostly Serbian, Ukrainian and Romanian nationals, convicted of human-trafficking, the directorate of prisons said on Wednesday in a reply to Reuters questions.
Citing overcrowded prisons, 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.
The move drew a protest from neighbouring Austria, a top destination for smuggled migrants heading for the heart of the European Union via Hungary from the Balkans. Vienna said it regards the release of human traffickers as a security threat.
The Hungarian prison directorate (BvOP) said there were 2,636 people convicted of human trafficking in Hungarian prisons, of whom 808 were foreign citizens eligible for the release.
"Incarcerating foreign nationals costs Hungarian prisons billions of forints each year," the BvOP press office said in its emailed reply.
It said that if those released do not leave Hungary's territory within 72 hours and are caught by police, they would have to remain in prison for the full term of their sentence.
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 on its southern border with Serbia.
Once in Hungary, migrants can move across generally open borders within Europe's Schengen zone to wealthier western EU countries like Austria or Germany.
(Reporting by Krisztina Than and Boldizsar Gyori, editing by Mark Heinrich)