Article 793 Federal Labor Law

When the declarant for his own facts no longer works for the enterprise or establishment, upon prior verification of the fact, the party offering the evidence shall be required to provide the domicile where he must be summoned. In the event that the offering party does not know the domicile, he shall make it known to the Court before the date set for the holding of the Trial Hearing at which the evidence is produced; the Court may request the enterprise to provide the last domicile it has registered of said person. In the event that the person referred to in this article has ceased to render his services to the enterprise for a term longer than three months, the evidence shall change its nature to testimonial.

If the person summoned does not appear on the day and hour set, the judge shall assess the pertinence of the evidence in relation to the facts in dispute, and may reject it if he considers that it is irrelevant to clarify them or that the difficulty of its production is the reason for the unjustified delay of the procedure.