Legal provisions for optional referendums at national level

Montenegro
Law on Referendum (2001)
http://www.legislationline.org/documents/id/3934
Article 3
The republican referendum can be called for the purpose obtaining anopinion of citizens prior to making a decision on specific issues lying withinthe competence of the Assembly of the Republic.
Constitution 2007
https://www.constituteproject.org/constitution/Montenegro_2007.pdf
Article 82: Responsibility
The Parliament shall:
1. Adopt the Constitution;
2. Adopt laws;
3. Adopt other regulations and general acts (decisions, conclusions,resolutions, declarations and recommendations);
4. Proclaim the state of war and the state of emergency;
5. Adopt the budget and the final statement of the budget;
6. Adopt the National security strategy and Defense strategy;
7. Adopt the Development plan and Spatial plan of Montenegro;
8. Decide on the use of units of the Army of Montenegro in theinternational forces;
9. Regulate the state administration system;
10. Perform supervision of the army and security services;
11. Call for the national referendum;
12. Elect and dismiss from duty the Prime Minister and members of the Government
13. Elect and dismiss from duty the President of the Supreme Court, thePresident and the judges of the Constitutional Court;
14. Appoint and dismiss from duty: the Supreme State Prosecutor andState Prosecutors, the Protector of human rights and liberties (Ombudsman), theGovernor of the Central Bank and members of the Council of the Central Bank ofMontenegro, the President and members of the Senate of the State Audit Institution,and other officials stipulated by the law;
15. Decide on immunity rights;
16. Grant amnesty;
17. Confirm international agreements;
18. Call for public loans and decide on credits of Montenegro;
19. Decide on the use of state property above the value stipulated bythe law;
20. Perform other duties stipulated by the Constitution or the law.
Article 91: Decision-making
The Parliament shall decide by majority vote of the present Members ofthe Parliament in the session attended by over one half of the total number ofMembers, unless otherwise regulated by the Constitution.
With the majority vote of the total number of Members the Parliamentshall adopt the laws that regulate: manner of exercise of liberties and rightsof the citizens, Montenegrin citizenship, electoral system, referendum,material responsibilities of the citizens, state symbols and use of statesymbols, defense and security, the army, establishment, merger and abolition ofmunicipalities; proclaim the state of war and state of emergency; adopt thespatial plan; adopt the Rules of Procedure of the Parliament; decide on callingfor the state referendum; decide on the reduction of the mandate; decide on theremoval of the President of the Republic from office; elect and dismiss thePrime Minister and members of the Government and decide on the trust in theGovernment; elect and dismiss the President of the Supreme court, presidentsand judges of the Constitutional court; appoint and dismiss the Protector ofhuman rights and liberties.