If you operate in Mexico or extend credit to Mexican counterparties, you will likely rely on promissory notes (pagarés). I see this structure used routinely in commercial practice. A recent decision from the Mexican Supreme Court changes how reliable those instruments are in litigation.
A company filed a summary commercial action to collect on six promissory notes. The documents met all legal requirements. They contained the debtor’s signature. From a formal standpoint, the claim looked solid.
The defendant, a university, denied the authenticity of the signatures attributed to its legal representatives. It submitted an expert handwriting analysis to support that position.
Both parties produced expert opinions. The conclusions were directly opposed. One expert validated the “undisputed” signatures used as a reference for comparison but concluded that the signatures on the promissory notes were false. The other expert reached the opposite conclusion.
Even though the university was ultimately released from payment, a constitutional (amparo) court held that experts could not challenge the “undisputed” reference documents. If they did, their opinion would automatically lose evidentiary value. ¹
On May 6, the Supreme Court of Justice of Mexico (the Court) disagreed with that approach.
This decision has direct implications for any company that uses promissory notes in Mexico as part of its commercial operations.
Why this decision matters
In its decision ², the Supreme Court clarified a key point: so-called “undisputed” signatures are not absolute truth. They are only a reference tool to compare against contested signatures through expert evidence, such as forensic handwriting analysis.
When the authenticity of a signature is challenged, the judge must evaluate all available evidence. This evaluation must follow principles of logic, sound judgment, and experience. It includes expert reports that question the reliability of the reference signatures themselves.
In practical terms, a judge cannot disregard an expert opinion simply because it challenges the signatures offered as undisputed.
Before this decision, the party submitting undisputed signatures as evidence had a procedural advantage. The opposing party had limited ability to attack those reference documents. That advantage is now reduced. The focus shifts to the quality and consistency of the signature process behind the documents.
From a business perspective, this is a material change. It affects how enforceable your credit documentation may be if a dispute arises.
Where is the main risk?
In Mexico, promissory notes are widely used. I see them in credit sales, leases, supply agreements, and deferred payment structures. They are simple to prepare. They are familiar to counterparties. They are considered standard practice.
What companies often do not control is the process used to obtain the signatures.
That process is now critical.
Whether you are the creditor, the debtor, or an unconditional guarantor, you should be able to answer a few basic questions with precision.
1. Did the person who signed have the right authority?
This is the first point I review in any enforcement scenario.
A power of attorney to execute negotiable instruments must comply with specific legal requirements. If there is a defect in how the power was granted, in its scope, or in its validity at the time of signing, enforcement can fail. This is true even if the underlying obligation is real.
If the power is used for an indefinite number of transactions, it must be registered with the Public Registry of Commerce.
Separately, directors may have authority to sign promissory notes by virtue of their appointment, subject to the company’s bylaws. In those cases, the company must verify that their appointment was valid at the time of signing and that their powers were not limited or revoked.
2. Are the signatures consistent?
This is a practical issue that becomes a legal problem.
In many transactions, documents are signed under time pressure. Multiple documents are executed in sequence. Fatigue and haste lead to variations in how signatures are written.
Those variations can be used by the opposing expert to argue that a signature is not authentic.
3. Do you have traceability over the signing process?
The company should have internal records showing who is authorized to sign, when those powers are exercised, and how each promissory note relates to the underlying transaction.
If there is no clear link between the note and the contract it supports and no record of how the signature was obtained, the company creates space for doubt. That doubt can be exploited in litigation through expert opinions.
What changes in practice
Before this Court’s decision, a formally valid promissory note with a signature that appeared legitimate gave creditors a strong position in a summary commercial action.
Now, the analysis goes deeper.
If the signature on the main contract—such as a credit agreement, loan, or lease—offered as an “undisputed” reference shows inconsistencies when compared to the signatures on the promissory notes, the opposing expert can challenge both. Not only the notes, but also the reference document.
If the experts disagree, the judge must weigh all the evidence. There is no automatic preference for one type of document over another.
Bottom line for your operations
This decision does not eliminate the usefulness of promissory notes. They remain a valid and widely used instrument in Mexico.
What it does is shift the risk.
The strength of your position will depend less on the formal validity of the document and more on the integrity of your signing process and your document control.
Good faith with your counterparty is not relevant once you are in court. What matters is what you can prove and how consistent your documentation is under technical scrutiny.
Many companies only identify these weaknesses after a dispute arises and a cost has already been incurred.
If you rely on promissory notes in Mexico, this decision is a practical example of what can happen in litigation. The formalities that may seem excessive today are often what determine whether you will be able to collect tomorrow.
For any questions or comments, feel free to contact us at acervantes@ceglegal.com
1. Articles 1250 Bis and 1250 Bis 1 of the Mexican Commercial Code regulate the procedure to challenge the authenticity of documents through expert handwriting analysis. Comparison requires “undisputed” signatures as reference, meaning documents acknowledged by the party to whom they are attributed, signed before a notary public, or submitted by that party in the proceedings. In ADR 7776/2025, the Supreme Court clarified that their “undisputed” character does not make them immune from scrutiny when expert reports themselves reveal inconsistencies. The judge must assess all evidence and cannot automatically disregard an expert opinion that questions those reference signatures.
2. Amparo Directo en Revisión 7776/2025