This study addresses the prescriptions of communication in organizational context in dialogue with the principles of the rationalization of labor relations, diffused in the first half of the twentieth century. In particular, it focuses on the analysis of the dictates of public relations accepted and disseminated by the discourse of the Instituto de Organização Racional do Trabalho (IDORT). At the time, the use of communication articulated by the ideals of public relations indicated the proposition of regulations for the administration of labor relations in organizations that was considered suitable by the managing class interested in the industrialization process of the country. IDORT, whose doctrine was based on the precepts of the “Scientific Organization of Work”, established by philosophies of taylorism/fordism and the movement “human relations”, acknowledged the idea of appeasement of social tensions in the workplace mobilized by ideals of public relations; a convenient proposal to the rationalization process of work in organizations. From this perspective, the thesis set out to study the prescriptions of communication in organizations in relation to the principles of rationalization of work, whose thought guided the main logic of organization and management of the work during the years 1930-1960, based on the discourse of IDORT. Through a theoretical and methodological approach that involved an extensive archival research, a survey of key documents was conducted to know the institutional trajectory of IDORT – their interests and their political and social positions – and the teachings of public relations shared and legitimized by IDORT. In this case, the material was analyzed to know the social, historical and ideological roots of prescriptions of communication. The corpus of research focused on three types of materials: texts of the IDORT’s institutional magazine, handouts of public relation’s courses promoted by the Institute and texts about public relations published by two institutions in France similar to IDORT. Especially in the 1950’s and 1960’s, two French entities that diffused the rationalization of work, were also interested in the philosophy of public relations and recognized its dictates. The analyzes of the study demonstrate the plausibility of the two hypotheses that guided the thesis: the development of public relations activity in Brazil was influenced by the principles of rationalization of work accepted by IDORT and the genesis of the prescriptions of communication in labor relations in organizations is correlated direct with the same principles.