In the view of trace the roots of labor law, the essay begins with an analysis of the theological foundations of the just wage. The historical re-reading of several social encyclicals testifies the refusal by the Magistery of the Church of the mercantilist conception of the work and the importance of some principles that could allow the "just" determination of the retributive performance. The principle contained today in the article 36 of the Italian constitution is then interpreted as the formalization from the legal system of an ethical judgement on the one hand and, on the other hand, as a rule able to establish and explain the specialty of labour law paradigm.