New mexico constitution
Article VII: elective franchise
Section 5

(1) a municipality that has not adopted a charter pursuant to Article 10, Section 6 of the constitution of New Mexico may provide by ordinance for runoff elections;
(2) a municipality that has adopted a charter pursuant to Article 10, Section 6 of the constitution of New Mexico, and prior to the adoption of this amendment the charter provided for runoff elections, shall hold runoff elections pursuant to the charter; or
(3) a municipality that adopts or has adopted a charter pursuant to Article 10, Section 6 of the constitution of New Mexico may, subsequent to the adoption of this amendment, provide for runoff elections as provided in its charter.