Fiscal Materiality: What It Is, Why Mexico's SAT Demands It, and How to Protect Your Business

Having the invoice and the proof of payment is no longer enough. If the SAT comes knocking and you cannot prove that the transaction behind that invoice actually took place — with signed contracts, deliverables, work logs, communications, and evidence with a verifiable date — your deductions are at risk.

This is called fiscal materiality, and since the reform of Article 69-B of the Federal Tax Code (CFF), it is the difference between a valid deduction and a transaction that the SAT can presume to be simulated.

In this article we explain what materiality is, what evidence the SAT requires, what happens if you don't have it, and how you can build solid evidentiary case files without relying on notaries or manual processes.

What is fiscal materiality

Materiality is the economic substance behind a transaction. It is not a new concept — it has always existed in tax law — but it gained practical relevance when the SAT began using Article 69-B of the CFF to combat the invoicing of simulated operations (colloquially known as "shell invoicing companies" or EFOS).

In simple terms: if you hire a consulting service for $500,000 MXN, the SAT wants to see evidence that the consulting actually took place. Not just the invoice and the payment, but the signed contract, the deliverables, the meeting minutes, the emails, the progress photos if applicable, and any other evidence proving that there was real economic activity behind that expense.

The invoice alone is no longer sufficient proof. It is merely the accounting record of something that must be independently demonstrable.

What Article 69-B of the CFF states

Article 69-B establishes that when the SAT detects that a taxpayer has issued tax receipts without having the assets, personnel, infrastructure, or material capacity to provide the services or produce the goods covered by those receipts, it may presume that the operations are nonexistent.

The key word is presume. Once the SAT presumes nonexistence, the burden of proof is reversed: it is no longer the SAT that must prove the operation is fake, but you who must prove it is real.

And proving it is real means presenting materiality evidence: documents proving that the service was rendered, that the goods were delivered, that the people involved exist and participated, and that everything occurred on the declared dates.

The problem of date certainty

This is where most companies fall short. Suppose you have a service agreement dated January. The SAT audits you in July and asks to see the contract. You present it. But the SAT argues: "How do I know you didn't fabricate this contract yesterday and put January's date on it?"

It is a valid argument. A Word document with a printed date proves nothing about when it was actually created. Anyone can fabricate a contract today and put whatever date they want on it.

Date certainty is a legal concept that resolves this. A document has date certainty when an independent mechanism proves its existence at a specific point in time. Traditionally, this was achieved through public registry inscription, submission to an authority, notarial attestation, or certified mail.

The problem is that these mechanisms are expensive, slow, and do not scale. Nobody is going to notarize every email, every progress photo, every meeting minute.

Blockchain as date certainty: Article 350 of the CNPCF

Mexico's National Code of Civil and Family Procedures (CNPCF), in its Article 350, establishes that information generated, communicated, received, or archived through blockchain or other distributed ledger technologies constitutes full proof.

This means that a document whose digital fingerprint (SHA-256 hash) is registered on a public blockchain has the same evidentiary weight as a public deed or a notarial instrument. And if someone challenges that proof, the burden of demonstrating that the blockchain was compromised falls on the challenger — something practically impossible given the nature of decentralized public networks.

In practice, this opens the door to sealing any digital document with verifiable date certainty, at a fraction of a notary's cost and in seconds instead of weeks.

How to build a materiality case file

A complete materiality case file typically includes:

Core documents (require e.firma SAT electronic signature): The service or purchase agreement, signed delivery acceptances, purchase orders, and amendment agreements. These documents must be signed with the SAT's e.firma to irrefutably link the signer to their RFC (tax ID).

Supporting documents (require date certainty): Progress photos, relevant emails, meeting minutes, work logs, screenshots, internal reports, and any other evidence that the operation took place. These do not require electronic signatures but do need date certainty so the SAT cannot argue they were fabricated after the fact.

Accounting documents (require maximum protection): The CFDI invoice, the proof of payment, and the final case file package. The main contract and the final package benefit the most from a NOM-151 certificate issued by a Certification Service Provider accredited by the Ministry of Economy.

The key insight is that not all documents need the same level of protection. Of a typical case file with 14 document types, perhaps only 2 need a NOM-151 certificate. About 6 require electronic signature with e.firma. And the remaining 6 only need blockchain sealing for date certainty. This makes protecting complete case files feasible without prohibitive costs.

What happens if you lack materiality

If the SAT audits you and you cannot demonstrate the materiality of your operations, the consequences are severe:

Disallowed deductions. The SAT can reject the entire deduction, generating a tax credit for unpaid income tax plus inflation adjustments, surcharges, and penalties.

EFOS presumption. If the pattern repeats with multiple suppliers, the SAT can include you on the Article 69-B blacklist as a company deducting simulated operations.

Criminal liability. In serious cases, tax fraud through simulated operations can constitute a criminal offense, with prison sentences.

The cost of an adverse audit is incomparably greater than the cost of protecting your documents with date certainty from the moment they are generated.

How SureSeal solves this

SureSeal is a Leeuwwolk platform that allows sealing digital documents with three levels of protection:

Level 1 — Blockchain: The document's digital fingerprint is registered on Polygon (a public blockchain). It proves the document existed on that date with that exact content. Ideal for photos, emails, meeting minutes, work logs.

Level 2 — e.firma + Blockchain: In addition to blockchain sealing, the signer uses their SAT e.firma, linking their RFC to the document. Ideal for contracts, delivery acceptances, purchase orders.

Level 3 — e.firma + Blockchain + NOM-151: A certificate issued by a Certification Service Provider accredited by Mexico's Ministry of Economy is added. Ideal for main contracts and final case file packages.

Sealed documents are grouped into projects that form complete materiality case files, ready to present to the SAT, auditors, or a court. Verification is public: anyone can verify a document by scanning a QR code, without uploading the file to any server.

→ Learn about SureSeal and protect your operations' materiality

Leeuwwolk is a Mexican company specializing in private artificial intelligence and digital signature solutions. Our products process data locally, without sending information to third-party servers.