The study focuses on the life of the “Union Departementale” (“UD”) of the Loire CFDT CFTC. This “UD” since 1947 has been part of the minority of the CFTC and gradually left the Christian community to integrate the working classes. It has fought against the war in Algeria, supported the secularization of the CFTC, worked together with the DU CGT, which wasmuch more powerful than itself. It has supported with enthusiasm the May-June 1968 movement and called for "three pillars" of the CFDT in 1970. In the 1970s, it has tried to encourage and support the development of workers' struggles and the various protest movements. In 1974, many of its militants have joined the socialist party that some left quickly afterwards.In 1976, the “UD” has opposed to the confederation in a "contribution" for the transition to socialism rejected at the Annecy conference. Similarly, it has opposed to the "refocusing" of 1978, before accepting the "re-unionization" in 1979.But since 1974, the “UD” has faced the economic crisis causing unemployment and deunionization starting in 1977. This crisis has worsened in the 1980s with the break with the “UD” CGT and internal conflicts with the confederation bringing it to inaction. In 1987, the election of a new Secretary General has marked a return to action, but the “UD” has remainedunable to conduct mass actions.The thesis proposes to look into the evolution of the confederation and the life of the “UD”, the elements for understanding its development from 1944 to 1973 and its deep crisis in the 1980s.