Short answer. Article 282 of the Labor Code ties its fraud ground to trust reposed by the employer, and its crime ground to offenses against the employer or immediate family. Fraud aimed only at a coworker does not, on its face, fit either wording, so the statute alone does not clearly answer whether it is a just cause.
What the law says
Fraud or willful breach by the employee of the trust reposed in him by his employer or duly authorized representative; Commission of a crime or offense by the employee against the person of his employer or any immediate member of his family or his duly authorized representatives
Labor Code, Article 282 — Just Causes For Dismissal. Read the full provision →
What the fraud clause is actually tied to
Article 282 does not make fraud in general a just cause for dismissal. It makes fraud or willful breach by the employee of the trust reposed in him by his employer or duly authorized representative a just cause — the trust that was breached has to be trust the employer placed in the employee, or trust placed by someone the employer has duly authorized to stand in its place. A coworker with no such authority is not, by this wording, the source of the trust the article is protecting.
The crime clause has the same limit
The neighboring ground in the same article covers commission of a crime or offense by the employee against the person of his employer or any immediate member of his family or his duly authorized representatives. Again the list is specific: the employer, the employer's immediate family, or the employer's duly authorized representatives. An ordinary coworker, sitting outside that list, is not covered by this clause either, unless that coworker also happens to hold a role the employer has duly authorized to represent it.
Where the statute genuinely does not resolve it
This is the honest gap: fraud committed against a fellow employee, without more, does not fall cleanly inside either named ground as written. Whether it could still be treated as a just cause would depend on facts this article does not itself supply — for instance, whether the coworker held a supervisory or representative role for the employer, or whether the conduct is treated as falling under the article's separate catch-all for other causes analogous to the foregoing. The bare text of Article 282 does not spell out how that catch-all applies to coworker-directed fraud, so no confident answer can be drawn from the statute alone.
What to do with an honest gap like this
Because the outcome turns on how your specific facts map onto trust, authority, and the workplace relationship involved, this is exactly the kind of question where a general summary of the law risks giving false confidence. Write down who the coworker was, what role — if any — they held over you or on the employer's behalf, and how the alleged fraud affected the employer's own interests, since those details are what any assessment of your situation would actually turn on.
Given how narrowly Article 282 defines these two named grounds, do not assume a dismissal notice invoking "fraud" automatically fits the statute simply because the word fraud was used.