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

Palau
Constitution of the Republic of Palau (1979) http://www.palauembassy.com/Documents/ConstitutionE.pdf
ARTICLE XIV
AMENDMENTS
Section 1. Anamendment to this Constitution may be proposed by a Constitutional Convention,popular initiative, or by the Olbiil Era Kelulau, as provided herein:
(a) at leastonce every fifteen (15) years, the Olbiil Era Kelulau may submit to the votersthe question: “Shall there be a Convention to revise or amend theConstitution?”. If a majority of the votescast upon the question is in the affirmative, a Constitution Convention shallbe convened within six (6) months thereafter, in a manner prescribed by law;
According to the Constitution of the Republic of Palau (ArticleXIV s 1(a)) the national legislature (Olbiil Era Kelulau) may, once every 15years, ask the people if they wish a general Constitutional Convention to beheld. Otherwise any constitutional reform proposal from any source requires amandatory final referendum on the proposal.