Who can initiate an optional referendum at the national level?

Constitutionof Republic of Moldova:

http://aceproject.org/ero-en/regions/europe/MD/the-constitution-of-moldova-2000/at_download/file

Article141.

Initiativefor revising the Constitution

(1)A revision of the Constitution may be initiated by:
(a)a number of at least 200,000 voting citizens of the Republic of Moldova.Citizens initiating the revision of the Constitution must cover at least ahalf of the territorial-administrative units of the second level, and in eachof these units must be registered at least 20000 signatures in support ofthe said initiative;

(b)a number of at least a third of the Parliament members;

(c)the Government.

(2)Constitutional law drafts shall be submitted to Parliament only alongside withthe Constitutional Court advisory opinion adopted by a vote of at least 4judges.

Article142.

Limitsof revision

(1)The provisions regarding the sovereignty, independence and unity of the State,as well as those regarding the permanent neutrality of

theState may be revised only by referendum based on a majority vote of theregistered voting citizens.

(2)No revision shall be performed, if it implies the infringement of fundamentalrights and freedoms of citizens, or their guarantees.

(3)The Constitution may not be revised under a state of national emergency,martial law or war.

Article143.

Lawon the Constitutional Amendment

(1)Parliament shall be entitled to pass a law on the amendment of Constitutionfollowing at least 6 months from the date of the corresponding initiative launch. The lawshall be adopted by a vote of two-thirds of the Parliament members.

(2)If, within a year from the date when the initiative on the amendment ofConstitution was launched, the Parliament has not passed the appropriateconstitutional law, the proposal shall be deemed null and void.