Mexico’s parties and electoral reform: PR seats and money

Between March 2025 and October 2026, Mexico’s Congress voted on five constitutional amendments about how officials are elected and who can stand. One failed: the electoral reform sent by the president, built around proportional representation seats and party funding. The other four were published in the Diario Oficial de la Federación (the official gazette): the ban on re-election and nepotism, the so-called “Plan B”, the annulment of elections for foreign interference and the single-nationality rule.

The first thing to know is that only one of them, the foreign-interference amendment, already applies to the federal election of 6 June 2027. The Constitution requires electoral laws to be published at least ninety days before the electoral process begins and forbids “fundamental legal changes” while it is under way (Article 105); the 2026-2027 federal process started in September 2026, and that amendment was published in June, before it. The others set their own start date or do not affect the federal election: single nationality counts from the 2028 process, and the nepotism and re-election bans from the 2030 processes.

This analysis looks at how each party voted on each amendment and where it stands on the underlying questions, using the test statements in the topics “Elections and parties” and “Institutions and corruption”. An asterisk (*) marks an estimated position: the party has not spoken directly on the question, and its position is inferred from what it has said on related matters. SOMOS and Partido PAZ were registered in 2026 and have no deputies, so they voted on none of these amendments; their positions come from their documents and statements and are provisional until they register their platforms in January 2027.

The five amendments at a glance

The reform that failed

The president’s initiative proposed two main things: that proportional representation seats stop coming from the lists drawn up by each party and go instead to its best-performing candidates, and a cut in public funding for parties. Amending the Constitution takes two-thirds of the deputies present (Article 135). On 11 March 2026, 494 deputies voted: the threshold was 330 and the reform got 259, 71 votes short (our own calculation from the Gazette’s roll-call vote).

It was not only the opposition that sank it. This is how each group voted (in favor / against / abstaining):

The PT and the PVEM, Morena’s coalition partners in 2024, voted almost entirely against. Their floor leaders did not object to spending less, but to how seats and money would be shared: the PVEM’s warned that handing proportional seats to the best-performing candidates would concentrate them in the states with the most voters, and the PT’s that it would shut out smaller states and “does create a democratic distortion for us.” Both offered instead to cut party funding by up to half, as long as it was shared out “equitably” (Expansión Política, 11 March 2026).

Proportional seats: lists or best performers?

Of the statements in this analysis, this is the one that most divides Morena from its allies. Morena strongly agrees that proportional representation deputies should be chosen by direct vote; it campaigned for the reform under the slogan “No to hand-picked proportional seats.” At the other end is the PVEM, which strongly disagrees: its condition was that the current system of proportional candidacies should not be changed.

The PT, the PRI and Movimiento Ciudadano disagree: all three voted against the reform, the PRI’s program of action defends the mixed system and Movimiento Ciudadano’s 2024 platform defends proportional representation. The PAN is the least obvious case: it voted against the reform as a whole, but in January 2026 its national leader said the party could accept proportional seats coming from the vote rather than from lists, so its position is agrees.

SOMOS disagrees: its documents call for keeping the mixed system, and in March its president rejected letting voters choose within the lists because it would “institutionalize the cheat sheets,” although in January the party had floated it as an option. Partido PAZ does not address it in its documents: neutral*.

Party funding

The Constitution sets public funding for parties with a formula: the number of people on the electoral register multiplied by 65% of the daily value of the UMA, Mexico’s unit of account. Of that pot, 30% is shared equally and 70% according to votes in the last election for deputies (Article 41). Two statements in the test deal with that formula: whether the pot should be cut, and whether it should be shared equally.

On the cut, only Morena strongly agrees: its 2024 platform proposes to “significantly reduce the very high cost” of elections, and its group voted for the reform that did so. The PAN disagrees: in January 2026 its national leader warned that cutting funding without stronger oversight “does not fight corruption: it legalizes it.” SOMOS, whose reform proposal says it is “not about cutting costs or weakening public funding,” also disagrees.

In the middle, neutral, are the PRI, the PVEM, the PT and Movimiento Ciudadano, each for its own reason. The PRI’s program of action calls for cheaper campaigns, yet it voted against the 2026 cut. The PVEM and the PT would accept cutting up to half only if the money were shared equitably. Movimiento Ciudadano’s national leader said in 2021 that parties should get less, and in 2026 its group voted against. Partido PAZ does not discuss the issue: neutral*.

Equal sharing is one of the tie-break questions (those the test uses only to separate tied parties), and five of its eight positions are estimated. The documented ones belong to the parties that ask for it: the PVEM, which strongly agrees, has proposed it for years; the PT, which agrees, asked for it for both money and radio and TV airtime; SOMOS, which agrees, proposes moving from today’s 30/70 to a 50/50 split, more equal without reaching equal shares.

Over-representation

The Constitution bars any party from having more than 300 deputies or a share of the Chamber more than 8 points above its share of the vote (Article 54). The cap applies to each party, not to the coalition, which in 2024 allowed the coalition of Morena, the PT and the PVEM to exceed two-thirds of the Chamber: how it was calculated, with the figures, is in the analysis “How Mexico elects its 500 federal deputies in 2027”.

The test asks whether no party should hold a larger share of deputies than of votes. The PAN strongly agrees (its Senate leader summed it up in 2026: “If you got 54%, you are entitled to 54% of the seats”), as do Movimiento Ciudadano, whose platform calls for preventing the over-representation of parties and coalitions, and SOMOS, which proposes scrapping the 8% margin. The PRI agrees: its platform calls for votes and seats to match as closely as possible, and its program of action for the cap to be extended to coalitions.

Morena, the PT and the PVEM have not spoken on this, and their positions (disagree*) are estimated: none of their documents proposes removing the margin, and the three form the coalition that exceeded two-thirds in 2024. Those three cells should be read with that caution in mind. Partido PAZ, agrees*, is also estimated.

“Plan B”: councils, legislatures and pay

A month after the rejection came a shorter amendment, which did pass: the Chamber approved it on 8 April 2026 by 377 votes to 102, and it was published on 23 April (DOF). It sets a maximum of 15 councilors per municipal council, applying from each municipality’s next term (councils that already have fewer keep them); limits each state legislature’s budget to 0.70% of its state’s budget; subjects the pay of electoral commissioners and judges to the ceiling in Article 127; and requires the Senate to cut its budget by 15% in real terms over four years. It does not touch proportional seats or party funding.

The split was different here: Morena, the PT and the PVEM voted in favor, as did Movimiento Ciudadano in general (26 to 0), although it then voted against the reserved articles; the PAN and the PRI voted against. In the test, the statement on these caps is another tie-break question: Morena, the PT and the PVEM strongly agree; Movimiento Ciudadano agrees; the PAN and the PRI strongly disagree. SOMOS (disagrees*) and Partido PAZ (neutral*) have not spoken on it; both defend the autonomy of municipalities and states in their documents.

Single nationality

Since the amendment published on 7 October 2026, the president, state governors and the head of government of Mexico City must be Mexican by birth and hold no other nationality: anyone who does must renounce it before registering as a candidate, and an office-holder may not use a foreign passport. Its transitional articles say it applies from the 2028 electoral process and not to those already in office (DOF): the 17 governorships elected on 6 June 2027 are not subject to it.

The Chamber passed it on 22 September 2026 by 334 votes to 116: Morena, the PT and the PVEM in favor; the PAN, the PRI and Movimiento Ciudadano against. That is why in the test the first three strongly agree with requiring single nationality to govern, and the other three strongly disagree. So does SOMOS, which declared its “total rejection” and asked the Senate to stop the amendment. Partido PAZ does not address it: neutral*.

Nepotism and re-election

The 2025 amendment did two things: it bars anyone from running for an office held by their spouse or a close relative, and it ends consecutive re-election for legislators, mayors and municipal council members. Both apply from the 2030 electoral processes (DOF, 1 April 2025). In the 2027 election for federal deputies, therefore, sitting deputies can still seek re-election, and the Constitution does not yet bar their relatives from running (the 2026 “Plan B” did not touch Article 55, which sets the requirements to be a federal deputy).

In general, the Chamber passed the amendment unanimously, with 477 votes. The difference was over the date. Movimiento Ciudadano voted against the reserved articles (0 to 26) because it wanted the nepotism ban to apply in 2027, as its floor leader, Ivonne Ortega, put it: it should “take effect from the 2027 election.” In the test it strongly agrees.

Morena, the PAN and the PRI agree with bringing it forward, by different routes. Morena voted for the 2030 date in the Constitution, but in May 2025 its National Council barred its own candidates from succeeding a relative as early as 2027. The PAN’s floor leader offered the group’s votes to move it back to 2027 (“we bring it back to 2027”), and the PRI asked for it to apply sooner; both ended up voting for the bill with 2030. On the other side, the PVEM (strongly disagrees) made its vote conditional on the ban waiting until 2030 and did not adopt Morena’s own veto, and the PT (disagrees) kept open the option of nominating relatives in 2027: “We are independent parties,” its floor leader said. SOMOS (agrees*) criticizes nepotism in its documents but has not spoken on the date, and Partido PAZ (neutral*) does not address the issue.

The one that counts in 2027: foreign interference

Since the amendment published on 2 June 2026, Article 41 of the Constitution adds one more ground for annulling an election: that “acts of foreign intervention or interference that influence the electoral results are proven.” It was published before the electoral process began, so it applies to 6 June 2027; its transitional articles required the laws to be adapted before 5 June 2026.

The Chamber passed it on 26 May 2026 by 307 votes to 128, in an extraordinary session: Morena (234 in favor and one abstention), the PT (41) and the PVEM (32 in favor and one against) voted for it; the PAN (64), the PRI (37) and Movimiento Ciudadano (26) against. No statement in the test asks about it.

The positions in one table

Of the 56 positions, 16 are estimated, mostly on how funding is shared and on over-representation, plus all seven of Partido PAZ. Each documented position, with its source, is on each party’s page and on the topic pages.

What the data show

The electoral reform split the governing coalition: on proportional seats and money, the PT and the PVEM voted with the opposition rather than with Morena. On single nationality and “Plan B”, by contrast, the three voted together again. Nor is the opposition a bloc: Movimiento Ciudadano supported “Plan B” in general and was the only group to vote against waiting until 2030 to ban nepotism, and the PAN said it was open to changing how proportional seats are filled even though it voted against the reform that did so.

For anyone voting on 6 June 2027, the practical upshot is that seats and money follow the same rules as in 2024: 300 single-member district seats and 200 proportional seats from party lists, the same caps and the same party funding formula. What changes afterwards will depend in part on the Chamber that comes out of that election: these seven statements are in the test (three in the quick version and five in the full one; the other two in the tie-break).