Who can initiate an optional referendum at the national level?

Bolivia

Answer

President
Legislative majority
Registered electors

Source

Law 026 (June 30-2010) on the Electoral Regime [Ley 026 del 30 de junio de 2010 del Régimen Electoral]Articles 16 and 17http://aceproject.org/ero-en/regions/americas/BO/bolivia-ley-del-regimen-electoral-2012

Comment

Excluding the issues that require a mandatory referendum, the Executive, the Legislative and the citizens can only initiate one referendum during the term of government (five years)