Written for Mexico. This analysis applies to Mexican federal tax law — ISR (income tax), IVA (VAT) and SAT rules — and cites Mexican statutes. Amounts are in Mexican pesos (MXN).
When the SAT audits, it doesn't audit your intention: it audits your paperwork. Two identical companies, with the same legitimate operations, can walk out of an audit with opposite outcomes — and the difference is almost never the lawyer they hired at the end, but the file they built from the start. We call that file the tax dossier.
What the tax dossier is
It is the master file — organized and permanent — that supports your company's complete tax position: who it is, how it operates, why its structure is what it is, and the evidence behind every relevant transaction. It is not "the accounting" — the accounting records; the dossier proves. It has a single quality standard: that an outside reviewer, without knowing your company, can reconstruct and validate every relevant deduction using only what's in the file.
The five folders that make it up
- Corporate: minutes, up-to-date bylaws, powers of attorney, corporate books, controlling-beneficiary file, shareholders' protocol if one exists. The company's legal identity, with no gaps.
- Structural: the documented reason behind the architecture — business-reason memos for each company, merger, spin-off or intercompany transaction (art. 5-A of the CFF, the federal tax code), transfer-pricing studies where they apply, intercompany contracts signed and in force.
- Operational: substance (materiality) files for the relevant transactions: specific contracts, deliverables, evidence of execution and use, a file for each significant supplier with its compliance opinion and verification against the art. 69-B lists.
- Labor-tax: employment contracts, stamped (SAT-certified) payroll consistent with the CFDI (digital tax invoices) and contributions, compliance with REPSE (the registry for specialized-services providers) where there are specialized services — the front where reviews in recent years have been most aggressive.
- Judgment: the tax positions you took and their basis: working papers for relevant calculations (CUFIN, CUCA, loss carryforwards), opinions or reports that support important decisions, and the record of rulings or criteria applied.
How much of your dossier exists today — and how much would have to be rebuilt under pressure?
Our Tax Dossier review audits the five folders against your real operation, hands you a traffic-light map of your gaps and a closing plan prioritized by risk. It is the service with which we've defused the most contingencies before they ever existed.
Why building it beforehand changes the outcome
Review deadlines are unforgiving. A typical information request gives 15 days, extendable. Reconstructing five years of evidence for a supplier that has already closed, with employees who are no longer there, within that window, is a losing bet. The file built in real time costs hours; the one rebuilt under a request costs the full tax assessment, with inflation adjustment and late-payment surcharges that in 2026 run at 2.07% per month.
The burden of proof is yours. On deductions, credits and substance, whoever asserts must prove — and the one asserting is you. The SAT does not have to prove your transaction didn't exist; it falls to you to prove that it did. Without a dossier, that conversation starts out lost.
It deters as much as it defends. A company that answers a first request with a complete, orderly and consistent file changes the tone of the review. Auditors also manage their time: the indefensible taxpayer is more profitable than the shielded one.
Frequently asked questions
Is the tax dossier required by law?
As a single integrated concept, no — it's a methodology. But almost all of its content is individually enforceable: accounting records (art. 28 CFF), support for deductions (art. 27 LISR), controlling beneficiary (32-B Ter), substance (materiality) against art. 69-B. The dossier merely organizes what the law can already require of you.
How often is it updated?
Relevant transactions are documented as they happen; the corporate records, at each shareholders' meeting or change; and a general review once a year before the annual return. As a process, it's hours a month; as a rescue, it's months of crisis.
What happens if a review has already started and I have no dossier?
You work with what exists and reconstruct what can be reconstructed, with an evidence and deadline strategy. It is exactly the scenario where tax litigation and technical defense make the difference — but it is the expensive scenario. If you're there, the clock is running: reach out to us today.
Let's talk about your case
Every structure, every operation and every family is different. The first step is always the same: an honest diagnostic of where you stand. Message us on WhatsApp or call — a reply the same business day.