Who can initiate an optional referendum at the national level?

Art. 150, 177 sec. 4 Constitution

The people, through 50,000 citizens entitled to vote,have the right to a referendum for the abrogation of a law, and to request thePresident of the Republic to call a referendum on issues of special importance.The Assembly, on the proposal of not less than one-fifth of the deputies or onthe proposal of the Council of Ministers, can decide that an issue or a draftlaw of special importance be submitted to referendum.

The Assembly may decide, by two-thirds of all itsmembers, that a proposed constitutional amendment shall be voted on in areferendum.