Legal provisions for mandatory referendums at national level

Venezuela
Constitution of Venezuela (1999)
http://venezuelanalysis.com/constitution/
Article 70: Participation andinvolvement of people in the exercise of their sovereignty in political affairscan be manifested by: voting to fill public offices, referendum, consultationof public opinion, mandate revocation, legislative, constitutional andconstituent initiative, open forums and meetings of citizens whose decisionsshall be binding among others; and in social and economic affairs: citizen serviceorgans, self-management, co-management, cooperatives in all forms, includingthose of a financial nature, savings funds, community enterprises, and otherforms of association guided by the values of mutual cooperation and solidarity.
The lawshall establish conditions for the effective, functioning of the means ofparticipation provided for under the present article.
Article 342: The purpose of constitutionalreform is to effect a partial revision of this Constitution and replacement ofone or more of the provisions hereof, without modifying the fundamentalprinciples and structure of the text of the Constitution.
The initiative for a constitutional reform emanates fromthe National Assembly, by resolution approved by a majority vote of themembers, from the President of the Republic sitting with the Cabinet ofMinisters, or at the request of registered voters constituting at least 15% ofthe total number registered with the Civil and Electoral Registry.
Article 344: Once approved by theNational Assembly, the draft constitutional reform shall be submitted to areferendum within 30 days from its approval. The referendum shall pass on thereform as a whole, but up to one third of the same may be voted on separately,if at least one third of the National Assembly so agrees, or if in theinitiative for the reform, the President of the Republic or a number ofregistered voters equivalent to at least 5% of the total registered with theCivil and Electoral Registry so requests.
Article 345: The constitutionalreform shall be declared approved if the number of affirmative votes is greaterthan the number of negative votes. A revised constitutional reform initiativemay not be submitted during the same constitutional term of office of theNational Assembly.