Puerto Rico Constitution
Article VI - General Provisions
Section 1.

Section 1. The Legislative Assembly shall have the power to create, abolish, consolidate and reorganize municipalities; to change their territorial limits; to determine their organization and functions; and to authorize them to develop programs for the general welfare and to create any agencies necessary for that purpose.

No law abolishing or consolidating municipalities shall take effect until ratified in a referendum by a majority of the qualified electors voting in said referendum in each of the municipalities to be abolished or consolidated. The referendum shall be conducted in the manner determined by law, which shall include the applicable procedures of the election laws in effect when the referendum law is approved.