Based on an ethnographic research in two local unions (UL) of the CGT, this article examines trade unionism in precarious sectors of the job market (large retailers, nursing homes, industrial subcontracting). It shows that this activity participates in the practical politicization of the working classes by means of sustaining a class-based approach to social relations. This paper aims to explain the inner workings of the politicization process using an interactionist methodology and seeks to explore the ways in which the employees’ experiences of domination at the workplace as well as that of injustice and distrust towards their employers interact with the guidance provided by local unions. The purpose of this article is to show that militant ideologies are not so much expressed in explicitly political terms, but in moral styles and principles which take on a pragmatic dimension inasmuch as they can be easily channelled into action in the workplace. These principles could be summarized as follows: Trust in “the bosses” is not a given; only power struggle can help obtain satisfaction in dealing with them. These principles reflect an ethic and a practical sense of daily resistance to the employer, which the employees and local union activists refer to as “fighting back”.