Issues of sub-national referendums regulated at the national level

Constitution of1947 with Amendments through 2012

https://www.constituteproject.org/constitution/Italy_2012.pdf

Art 132

By a constitutional law, afterconsultation with the Regional Councils, a merger between existing Regions orthe creation of new Regions having a minimum of one million inhabitants may beagreed, when such request has been made by a number of Municipal Councilsrepresenting not less than one-third of the populations involved, and therequest has been approved by referendum by a majority of said populations.

The Provinces and Municipalitieswhich request to be detached from a Region and incorporated in another may beallowed to do so, following a referendum and a law of the Republic, whichobtains the majority of the populations of the Province or Provinces and of theMunicipality or Municipalities concerned, and after having heard the RegionalCouncils.