Legal provisions for optional referendums at national level

Cuba's Constitution of 1976 (last amended in 2002)

ARTICLE 75. The National Assembly of People’s Power is invested with the following powers:

[…]

u. calling for the holding of a referendum in those cases provided by the Constitution and others which the Assembly considers pertinent;

Cuba's Constitution clearly provides for obligatory referendum. But it is not very clear about the possibility of optional referendum. We based our decision on the wording of the Article 75, which regulates for the possibility of referendums for "other" cases "which the Assembly considers pertinent".