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

Uganda
CONSTITUTIONOF UGANDA (1995)
http://www.opm.go.ug/assets/media/resources/6/Constitution.pdf
Article 74. Change of political systems by referenda or elections.
(1)A referendum shall be held for the purpose of changing the political system-
(a) if requested by a resolution supported by more than half of allmembers of Parliament; or
(b) if requested by a resolution supported by the majority of the totalmembership of each of at least one half of all district councils; or
(c) if requested through a petition to the Electoral Commission by atleast one-tenth of the registered voters from each of at least two thirds ofthe constituencies for which representatives are required to be directlyelected under paragraph (a) of clause (1) of article 78 of this Constitution.
THE OTHER POLITICAL SYSTEMS ACT(2000)
http://www.ulii.org/ug/legislation/consolidated-act/262
Article 2. Acceptance ofpolitical system (Optional referendum)
No political system shall beaccepted as any other democratic and representative political system for thepurpose of article 69(2)(c) of the Constitution for being proposed for voting,at a referendum under article 74(1) of the Constitution, or for the purposes ofa resolution of Parliament under article 74(2) of the Constitution, unless thatpolitical system has, upon a petition, been approved by Parliament before thereferendum in question or the parliamentary resolution under article 74(2) ofthe Constitution.