The referendum question reads "Are you in favour of the law ratifying the arbitration agreement between the governments of Slovenia and Croatia, which was adopted by the Slovenian Parliament at its session of 19 April 2010, becoming valid?". Voters can circle either Yes or No on the ballot.

The result of the referendum is binding on the authorities. A majority of the Yes answers will mean that the arbitration agreement is finally confirmed and that its prior ratification in the national parliament is valid.

A turnout is not a prerequisite for declaring the referendum's outcome valid.

In the event of more No's than Yes's, the ratification in the Slovenian parliament would be considered null and void and it would not be possible for the government or parliament to raise this topic over the next year.

Preliminary results will be announced on Monday and final official results will be released on Tuesday.

Most opinion polls show that the Slovenians seem inclined to confirm the border arbitration agreement, however local political analysts warn that this referendum may be a cliff hanger.

In his efforts to persuade voters to support the deal, Prime Minister Borut Pahor has warned that the rejection of the document would push Slovenia into isolation and the international community would not understand such a move.

The Slovenian opposition has described Pahor's agreement with Croatian Prime Minister Jadranka Kosor, which they concluded in Sweden last year, as Croatia's victory in the battle over demarcation of the border line between the two neighbours.

Former Slovenian President Milan Kucan, former Croatian President Stjepan Mesic and former German Foreign Minister Joschka Fischer on Friday joined in calls for supporting the agreement.

They made statements in Slovenian newspapers calling on Slovenians to back the deal.