The professional identity of the employees of the Postal sorting offices can be understood in relationship to their working in an environment of organizational transformation. An analysis of their response to changes underway in the content of their work permits us to grasp the dynamic, contradictory element of their professional identity. This identity derives from the actual work performed, but also from « work » considered in its broader sense, which goes beyond simple activity and encompasses the way in which employees perceive, live, and give meaning to their work. Hence, throughout the 1970s and 1980s, we observe a reconstruction of professional identity as work loses meaning in the sorting offices, due in particular to the spread of mechanization but also to new, more precarious forms of employment. Such changes lead workers to envision participation in renewed social conflicts.