How is activist expertise regarding the use of strikes transmitted in France’s service sector ? To respond to this question, I draw upon ethnographic observation of the training and activist support work carried out by one of the CGT’s territorial labor union structures. In fact, in sectors lacking a robust tradition of labor union agitation, training for new activists in the techniques of labor union action mainly takes place in local spaces of labor union organization. I first consider the technical and political apprenticeships through which members are in various and competing ways initiated into the use of strikes. I then underscore the many factors that obstruct transmission of such practical activist expertise as well as the principles of activist action in the use of the strike. Two matters are thus considered here : on the one hand, the organizational limits of training labor union members in activist practices and the principles of action with which their confederation identifies ; on the other hand, the impediments to expanding strikes in professional domains characterized by a low rate of labor union participation.