The Supreme Court invalidates Tamaulipas' municipal reform due to the electoral blackout period

The Plenary of the Supreme Court of Justice of the Nation declared the total invalidity of Decree 66-1146, which reformed and added various provisions to the Municipal Code for the State of Tamaulipas, as it was promulgated and published within the legislative blackout period regarding electoral matters. The ruling, approved in the session of September 10, 2026, is published in the Official Gazette of the Federation on Wednesday, October 14, 2026 (No. 281/2026, Section I, p. 148) and resolves Unconstitutionality Action 93/2026 and its accumulated cases 95/2026, 100/2026, and 101/2026.

The challenged decree and the electoral calendar

Decree 66-1146 was published on July 1, 2026, in the Official Gazette of the State of Tamaulipas. It reformed articles 26, fractions IV, V, and VI, and 38, fraction X, and added a fraction VII to article 26 of the Municipal Code for the State of Tamaulipas, thereby modifying eligibility requirements for the composition of city councils and a cause for suspension or revocation of office.

The Electoral Institute of Tamaulipas (IETAM) informed the Court, via an official letter submitted on August 18, 2026, that the 2026-2027 ordinary electoral process would begin on Sunday, September 13, 2026. Based on this, the 90 days prior ran from June 16 to September 13, 2026, meaning the last day to promulgate and publish fundamental legal modifications in electoral matters was June 15, 2026.

The decree appeared 16 days after that deadline had expired: between its publication and the start of the process, 74 days elapsed, fewer than the 90 required by article 105, fraction II, penultimate paragraph, of the Political Constitution of the United Mexican States.

Who challenged and what they alleged

Four national political parties filed the lawsuits, all of which were admitted and accumulated:

• Labor Party (PT), lawsuit of July 20, 2026, signed by members of its National Coordinating Commission, including Alberto Anaya Gutiérrez.
• Institutional Revolutionary Party (PRI), lawsuit of July 29, 2026, presented by Rafael Alejandro Moreno Cárdenas as president of its National Executive Committee.
• National Action Party (PAN), lawsuit of July 30, 2026, presented by Jorge Romero Herrera as president of its National Executive Committee.
• SOMOS Political Party, lawsuit of July 30, 2026, signed by Guadalupe Acosta Naranjo.

The plaintiffs argued that the reforms constituted fundamental modifications in electoral matters and that they unduly restricted the right to be voted for and to remain in office, by making ineligibility or suspension dependent on a criminal process and pretrial detention without a final judgment.

The decision of the Plenary

The Plenary Court considered the concept of invalidity based on the violation of the legislative blackout period to be well-founded and determined that the decree is indeed applicable to the electoral process and that its changes are fundamental, as they alter the universe of persons who can be nominated, registered, or remain in office. The resolving points were:

• Unconstitutionality Action 93/2026 and its accumulated actions 95/2026 and 100/2026 were found to be admissible and well-founded.
• Unconstitutionality Action 101/2026 was dismissed due to the lack of standing of the party who promoted it on behalf of SOMOS.
• Invalidity of Decree 66-1146 in its entirety, with general effects starting from the notification of the resolutions to the Congress of the Free and Sovereign State of Tamaulipas.
• Publication of the judgment in the Official Gazette of the Federation, the Official Gazette of the State of Tamaulipas, and the Judicial Weekly of the Federation.

The invalidity of Article 26, fractions IV, V, VI, and VII, was approved unanimously by nine votes; that of Article 38, fraction X, by a majority of six, with opposing votes from ministers Esquivel Mossa, Figueroa Mejía, and Guerrero García. The effects were approved by a majority of eight votes, with an opposing vote from President Hugo Aguilar Ortiz, who announced a clarifying vote. The project was prepared by the reporting minister Irving Espinosa Betanzo.

Without revival and with the current regulatory framework

The Court rejected restoring the previous text of the Municipal Code, noting that its constitutional regularity remains undefined because it was challenged in Unconstitutionality Action 55/2026 and its accumulated actions 57/2026, 58/2026, 59/2026, and 60/2026. It added that the invalidity does not create a regulatory vacuum, as the requirements to access popularly elected offices and the grounds for the suspension of political-electoral rights are based on Articles 35, 38, and 115 of the Federal Constitution, the Political Constitution of the State of Tamaulipas, and local electoral legislation, regulations that remained untouched by the decree.

The resolution nullifies, prior to the election day, a set of eligibility requirements and grounds for suspension from office that would have governed the municipal contest in Tamaulipas. For readers, the ruling confirms that electoral rules must be finalized and published at least 90 days in advance, and that the Court can completely annul a local reform when that constitutional deadline is not met.

Source: Official Gazette of the Federation, No. 281/2026, October 14, 2026, Section I (Judicial Branch), p. 148 (official reference: Unconstitutionality Action 93/2026 and its accumulated actions 95/2026, 100/2026, and 101/2026).