Issues in relation to which referendums are optional at the national level

The Constitution of the Republic of Mali (1992)http://unpan1.un.org/intradoc/groups/public/documents/cafrad/unpan002746.pdf

Article 41: The President of the Republic, by proposal of the Cabinet, during the duration of its sessionsor by proposal of the National Assembly, after the opinion of the Constitutional Court is published in the Official Journal, may place under referendum any and all questions of national interest, any law related to the organization of public powers, consisting of an approval of an accord of union or an authorization of a treaty which, without being unconstitutional, would have effect on the function of the Institutions.When the referendum has concluded that the proposal is to be adopted, the President of the Republic shall promulgate it in the manner prescribed in Article 40.