The aim of the article is, on the one hand, to analyze the content and scope of fundamental right to the protection of personal data, provided by art. 18.4 of the Spanish Constitution; on the other, to decline this right in the context of the employment relationship starting from the interpretation given by the Spanish Constitutional Court in judgment no. 39/2016. The contrast between this right and the freedom of enterprise, which is realized in the power of organization, control and supervision of work performance, is resolved by the Constitutional Court in the light of the principles of proportionality, suitability and necessity. The outcome of the balancing leads the Constitutional Court to establish the prevalence of the entrepreneurial freedom on the right to privacy of the employee.