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).
It's one of payroll's most common and worst-understood errors: the company religiously stamps every receipt, believes it has "already complied," and never remits the ISR it withheld. Stamping and remitting are not the same thing — and the difference, which the SAT detects on its own, can escalate from an adjustment to a criminal file. The employer's viewer lets you see it before the authority does.
Stamping ≠ remitting: the difference that costs dearly
When you pay a worker, you withhold ISR (art. 96 LISR): that money stops being theirs and stops being yours — it belongs to the treasury, and you merely hold it in trust until you remit it. Stamping the payroll CFDI documents the payment and the withholding. Remitting means paying that withheld ISR to the SAT in your return for the period. They are two separate obligations under art. 99 LISR: you can stamp perfectly and, even so, fail to remit. And that's the mental trap — the stamped receipt is not proof that you paid the treasury; it's proof that you withheld from the worker. The withheld money you don't remit sits in your account as if it were your own cash flow. It isn't.
The cross-check the SAT runs on its own (and the viewer shows you first)
The SAT doesn't need to audit you to detect this: every payroll CFDI reports the withheld ISR in real time, and all it takes is comparing that against the ISR you remitted in your withholding returns. If you stamped withholdings of 100 and remitted 70, the system sees a shortfall of 30 — without anyone reviewing a single invoice. The employer's payroll receipts viewer shows you that same figure: the accumulated ISR withheld according to your receipts. Cross-checking it yourself against what you remitted means asking yourself, for free and in private, the same question the authority would ask you — with the advantage of being able to answer it before it's ever posed.
From an administrative difference to a tax crime
This is where it stops being an accounting matter. Withholding taxes and failing to remit them is classified as equivalent tax fraud (art. 109, sec. II of the CFF), because you are using money the law entrusted you to hold for the treasury. It isn't the same as owing your own tax: it's using someone else's withheld money. That's why we put it among the three deadly tax sins — alongside floating the IVA (VAT) and buying invoices — the errors where the exposure isn't only financial, but criminal. And unlike other, interpretable tax matters, this one has no gray zone: you withheld, you didn't remit, the amount is objective.
How to fix it before the request
The good news is that the way out is clean if you get ahead of it. Remitting the missing withheld ISR on your own initiative — before any request or start of audit powers — lets you pay only the tax with adjustment and surcharges, with no penalty (art. 73 CFF), and defuses the criminal risk. The sequence: reconcile with the viewer what was stamped against what was remitted, quantify the shortfall by period, and remit it, adjustment and surcharges included, as soon as possible; if cash flow can't cover it in one go, installments are available. What can't continue is the drift: with each month that passes, the adjustment grows and the window for a voluntary correction stays open only until the first letter arrives. You can size up the cost of getting current with our surcharge calculator.
Frequently asked questions
Why is failing to remit a withholding so serious?
Because it isn't your money: when you withhold ISR from your workers, you hold in trust a resource that already belongs to the treasury. Using it is classified as equivalent tax fraud (art. 109-II CFF), with criminal consequences, not just financial ones. Owing your own tax is a problem; keeping money withheld from third parties is another one, far more serious.
How does the SAT find out if it hasn't audited me?
Through an automatic cross-check: every payroll CFDI reports the withheld ISR in real time, and the SAT compares it against what you remitted in your returns. The difference jumps out with no visit needed. The employer's viewer shows you the same accumulated withholdings, so you can run the cross-check yourself first.
Can I fix it without a penalty?
Yes, if you get ahead of it. Remitting the shortfall on your own initiative, before any request (art. 73 CFF), lets you pay the tax plus adjustment and surcharges, with no substantive penalty, and closes the criminal door. Once the request arrives, the price and the conversation change. That's why the key word is beforehand.
Does the employer's viewer show me the ISR I remitted?
No: the viewer shows what was stamped — the ISR withheld according to your receipts — not what you paid in your returns. That second figure comes from your withholding forms. Reconciliation is precisely cross-checking the two: what the viewer says you withheld against what you actually remitted. The difference is the shortfall to regularize.
Did you withhold payroll ISR that you haven't remitted?
It's the kind of difference best closed before the letter arrives, not after. We quantify the shortfall by reconciling the viewer against your returns, regularize it on your own initiative — tax, adjustment and surcharges, no penalty — and leave the process shielded going forward. The sooner, the cheaper and the cleaner.