An estimate 1.7 million voters will determine whether incumbent President Danilo Turk will remain in office, challenged by Prime Minister Borut Pahor, Radio B92 in Belgrade reported.
The most recent polls indicated Pahor had 55 percent support to Turk's 24 percent, the report said.
Both candidates have leftist political backgrounds, which hasn't gelled voter support as allegations of corruption emerged in recent weeks. Turk also sparked public anger by announcing federal budget cuts were inevitable.
Violent street protests in the capital, Ljubljana, and the central city of Maribor Friday resulted in at least 30 arrests and 25 people injured, the report said.
Slovenia was the first regional entity to secede from the former Yugoslavia in 1991 and wasn't part of the ensuing ethnic wars that engulfed Bosnia and Croatia.