To date, Slovenia has lent 263.68 million euros to Greece through two euro stabilisation mechanisms and issued an additional 1.55 billion euros as guarantees.
This accounts for a quarter of Slovenia's annual budget revenues, and Greece has so far repaid only EUR 17.6 million as interest.
Slovenian Foreign Minister Karl Erjavec said on Sunday that Ljubljana obviously had to forget its money lent to Athens.
He accused Greek Prime Minister Alexis Tsipras of pushing his country into a hopeless situation.
Greece is faced with a political crisis that will lead to early elections and even to the withdrawal of Greece from the 19-member eurozone.
The eurozone (euro area) is a monetary union of 19 European Union (EU) member states that have adopted the euro as their common currency and sole legal tender.
On the other hand, Slovenian Agriculture Minister Dejan Zidan, who is at the helm of the Slovenian Social Democrats (SD), said that the referendum was a legitimate right of the Greeks and added that EU leaders shared responsibility for the latest developments.
Prime Minister Miro Cerar on Saturday described the decision by his Greek counterpart to call a referendum as an unfair move which might be also perceived as an attempt to blackmail the EU.
President Borut Pahor has stated that this is a very serious situation and appealed for a compromise.