This paper seeks to specify the particularities of the reinforced protection regime that characterizes labor law in its substantive and procedural dimension of probation. In order to carry out this task, it takes as its starting point the well-known case of Madrid v. Sociedad de Profesionales Kronos. Based on the study of this case, in which new technologies and their application in labor environments becomes legally conflictive, it shows how the principle of worker protection extends its scope of influence to both substantive and labor law procedural. With respect to the first, the extended protective regime takes precedence over other rights through the protection of constitutional guarantees. Regarding the second (procedure of proof in labor law) the principle operates as a criterion of attenuation of the guiding principle of sound criticism (the free investigation of the truth of the facts), leaving in evidence that the labor legislator has taken into consideration values of an extra nature epistemic in the design of the labor probation system.