The theme of this article concerns the representation through collective actors. The article starts by addressing the soundness of the typical assumption held by labour economics reasoning which states that the differences in union behaviour depend on union membership composition. This approach fails to consider the distinctive features of a representation carried out by collective actors. The multiple dimensions involved in this type of representation correspond directly or indirectly to different theoretical discourses which are all analysed in the article. Such theoretical discourses regard representation (whith the main distinction between acting for and standing for), collective actors decisions, identities and recognition, performative powers, democratic internal structure of the actors, paradoxes of the collective action. This analytical framework allows to complicate ("à la" Hirschman) the economic discourse and to avoid the trap of the personification of the collective actors or the simple metaphorical use of the concept of actor, or subject.