Mexico's congress has passed a constitutional amendment that would allow election results to be annulled if foreign interference is found to have influenced the outcome — a move that has drawn fierce criticism from opposition politicians and electoral experts who warn it could be used to invalidate unfavourable results.

The bill, proposed by President Claudia Sheinbaum and her ruling Morena party, defines foreign interference broadly to include illicit financing, propaganda, the systematic dissemination of misinformation, digital manipulation, and the intervention of foreign governments or agencies. It was passed first by the lower house and then by the senate, and now requires ratification by a majority of Mexico's 32 states. Morena controls at least 23 statehouses, making eventual ratification likely. However, secondary legislation needed to put the amendment into practical effect was pulled from the agenda by Morena's own congressional leader, Ricardo Monreal, who said it required a longer period of reflection and broader parliamentary consensus. Legal experts note this leaves the constitutional change without an operational framework for now; if complementary laws are eventually passed, the reform would apply from the 2030 general elections.

Critics argue the amendment's sweeping language could allow virtually anything to be classified as foreign interference — a statement from a US official, an editorial in a foreign newspaper, or a report by an international NGO. Arturo Sarukhan, a former Mexican ambassador to the United States, called it "a blank cheque" for Morena. "This law doesn't prevent foreign interference," he wrote. "It hands the government a veto over election outcomes it doesn't like." Electoral specialist José Antonio Crespo described the original text as "so vague" that it could become an instrument of abuse, particularly by the governing party. Opposition senator Ricardo Anaya of the centre-right PAN party was more blunt: "It's a trap so that Morena can literally annul any election they want."

Sheinbaum has framed the measure in terms of national sovereignty, a sensitive issue at a time when Mexico faces significant pressure from the United States under President Donald Trump, who has repeatedly threatened intervention against Mexican drug cartels and whose administration has designated several cartels as terrorist organisations. Last month, US authorities indicted ten current and former officials from the northwestern state of Sinaloa, including its governor, over alleged ties to a major drug-trafficking organisation — a development that sent shockwaves through Mexico's political establishment.

The amendment's passage matters because Mexico holds midterm elections next year, in which all 500 seats in the lower house and hundreds of local offices will be contested — votes in which Morena could face a significant challenge to its current dominance of congress. Analysts point out that Mexico's electoral court, which would rule on any annulment, lost much of its independence under Sheinbaum's predecessor and is now seen as broadly aligned with the ruling party. "If they wanted, they could allege foreign intervention and the court would rule in their favour," said political analyst Carlos Bravo Regidor. The combination of broad legal language, a compliant judiciary, and approaching elections has made this one of the most contested pieces of legislation in recent Mexican democratic history.