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Two containers reach the same Mexican port on the same morning, carrying the same input from the same supplier. One clears at zero. The other owes 87,500 dollars before the cargo moves. Nothing about the goods explains the gap.
Since January 1, 2026, the general import duty on 1,463 tariff lines turns on a question the cargo cannot answer for itself: does the merchandise qualify as originating under one of the trade agreements Mexico has in force, and can that be proved at the moment the pedimento is presented. On a line that moved to 35%, a shipment with a customs value of 250,000 dollars carries 87,500 dollars in duty if the answer is no, and nothing if the answer is yes.
The wall is already up. What is still open, in most operations, is the file that gets you past it.
Three cost paths, and the arithmetic that separates them
Every affected shipment lands on one of three paths, and the distance between them is larger than most landed-cost models assume.
Path one: qualifying origin, documented. The good meets the rule of origin under an agreement Mexico has in force, and the certification is valid and in hand at despacho. The new rate never applies. Duty is whatever the agreement says, which for most industrial inputs is zero. This is the only path where the reform is invisible.
Path two: non-qualifying origin, definitive import. The good enters under the new rate, somewhere between 5% and 50% depending on the line. The duty itself is the headline, but it is not the whole number. Under Article 27 of the Ley del Impuesto al Valor Agregado, the base for import IVA is the customs value plus the general import duty and any other charges owed on the importation. A higher duty therefore lifts the IVA base with it. For most operations that IVA is creditable, so it is a cash-flow effect rather than a permanent cost, but it is working capital committed at the border rather than deployed in the business.
Path three: non-qualifying origin under a duty deferral program. This is the path most operations believe they are on, and it is the one most often misread. IMMEX defers the general import duty. It does not forgive it. The duty materializes on a change of customs regime to definitive, on a sale into the domestic market, and, for a large share of corridor manufacturers, on the export itself. More on that in a moment, because it is the part of this reform that reaches operations that never sell a single unit in Mexico.
What changed, and what did not
The instrument is a decree published in the Diario Oficial de la Federación on December 29, 2025, reforming the duty rates on 1,463 tariff lines of the Tarifa de la Ley de los Impuestos Generales de Importación y de Exportación. It took effect January 1, 2026. The Secretaría de Economía identified the covered sectors as automotive, textiles, apparel, plastics, steel, home appliances, aluminum, toys, furniture, footwear, leather goods, paper and cardboard, motorcycles, trailers and glass. Rates run from 5% to 50%, and they apply to merchandise from countries with which Mexico has no trade agreement in force.
Two things about the decree are worth stating plainly, because the coverage in January got both of them wrong in the same direction.
First, there is no expiry. The initiative sent to the Cámara de Diputados in September 2025 carried a horizon. The version that passed does not. The transitory articles of the published decree establish the date of entry into force, confirm that tariff lines not expressly modified continue at their existing rates, and abrogate anything that contradicts the decree. None of them sets an end date. Any plan built on the assumption that these rates lapse at the end of 2026 is a plan built against a draft that was superseded before publication.
Second, the decree left one door open on purpose. A transitory article authorizes the Secretaría de Economía to implement specific mechanisms and legal instruments for the importation of goods from countries with which Mexico has no trade agreement. That is the legal hook for import quotas and sector-specific relief. It is not a general exemption, and nothing about it is automatic. It means the schedule can move for a given sector, on the authority's timetable rather than yours.
Which path your operation is actually on
The reform is not a product question. It is a four-step file question, and most operations can answer the first two from data they already hold.
Is the line covered? Scope is set at the fracción arancelaria, not at the product family. A component you have imported at 5% for a decade can sit on the list while the finished good it goes into does not. Run your active classification master against the modified lines, not your product catalog.
Does the good qualify as originating? Qualification is per line, under the specific rule that applies to that line in the specific agreement you intend to claim. Mexico has agreements covering more than fifty countries, and the rule that governs a textile input is not the rule that governs a steel derivative. A supplier's assurance that the goods are "from a treaty country" is a statement about geography, not about origin.
Does the proof exist, and is it valid on the date of the pedimento? On paper, the decree exempts merchandise with qualifying origin, and the exemption sounds like a property of the goods. In practice, it is a property of the file. Merchandise that would have qualified perfectly, entered on a day when the certification had expired, been issued for the wrong period, or been signed by a party without authority, pays the full rate. The customs authority does not evaluate where the good was made. It evaluates what was declared and what supports it.
If the good does not qualify, which program actually moves the rate? Here the answers narrow fast. PROSEC reduces the duty on authorized inputs, but only for producers registered in the corresponding sector, and only for inputs used to manufacture the goods that sector covers. The Regla Octava mechanism, which allows qualifying inputs to enter under specific Chapter 98 headings, requires a valid permiso previo from the Secretaría de Economía and is assessed case by case. Neither is a general exemption available on request.
The part that reaches operations with no domestic sales
There is one interaction in this reform that does not appear in the decree at all, and it is the one that surprises IMMEX manufacturers.
Article 2.5 of the T-MEC governs drawback and duty deferral programs. Under it, when non-originating materials are temporarily imported into Mexico and incorporated into goods later exported to the United States or Canada, the duty exemption cannot exceed the lesser of two amounts: the Mexican duty owed on those non-originating materials, or the duty payable in the destination country on the finished good. The rule exists to stop a producer from collecting a benefit at both ends.
Read that against a schedule where the Mexican duty on the non-originating input just moved from 5% to 30%. The lesser-of calculation has a new floor. A maquiladora importing Asian inputs, transforming them, and shipping north has always run this analysis. What changed on January 1 is the number that goes into it. The exposure is created at the moment of the temporary import and settles on export, which is precisely why it escapes operations that think of the general import duty as something only definitive importers pay.
In our work across the corridor, this is where the reform is landing hardest and quietest. Across more than 190,000 customs operations a year at 39 ports, the pattern in the first half of 2026 has been consistent: the operations that modeled the increase were the ones importing for the domestic market, and the operations absorbing it without a line item for it were export manufacturers who assumed deferral meant exemption. The duty that shows up in a definitive pedimento gets budgeted. The one that surfaces through an Article 2.5 calculation gets discovered.
The moves that close the gap
Rebuild the origin file before the next purchase order, not the next audit. For every covered line, decide whether you are claiming preferential origin and assemble what supports it: the applicable rule, the qualification analysis, the certification, and the evidence behind the certification. A claim you cannot reconstruct twelve months from now is a contingent liability, not a saving.
Requalify at the supplier level, not the shipment level. If a supplier in a non-agreement country is the reason a line is exposed, the question is not how to document this shipment. It is whether an equivalent input is available from a country Mexico has an agreement with, at a total delivered cost that now includes 5 to 50 points of duty on the incumbent. That comparison looks different than it did in December.
Run the Article 2.5 exposure separately. For IMMEX and recinto fiscalizado estratégico operations exporting to the United States or Canada, model the lesser-of calculation on the new Mexican rates, line by line, and check whether PROSEC or a Regla Octava authorization moves the input rate enough to change the result. This is the single fastest place to find money in the current schedule.
The only line item you can still change
Duty rates are set by decree. Classification is set by the goods. Origin is the one variable in the equation that responds to how you build the file, and it responds only before the cargo moves.
That is the whole reform, stated as an operator would state it. The 1,463 lines are the price list. The certification is the discount, and it is not retroactive.
Talk to a Joffroy expert about an origin exposure review across your covered lines, including the Article 2.5 calculation for your export flows.
TRADE. UNDER CONTROL.
