This essay analyses the current Italian models of representative structure, as far as the trade union relationship system is concerned. The starting point is a survey of the role of constitutional provisions in this area. In the second place, the Author considers the influences engendered by these provisions on the enterprise models. A special attention is devoted to the solution embodied in article 19 of the 1970 Act - the so-called "Statuto dei lavoratori" -. This issue is examined taking into account both the time span before and after the 1995 referendum. This perspective is adopted in order to underline the trend followed by the system towards the correspondence between the recognition of the rights of employee representative groups and the exercise of the "bargaining " activity. Furthermore, the Author deals with the "bargaining model" which has been created by the trade unions with the "Protocollo" adopted in July 1993. In conclusion, the Author emphasizes that the limits of the model described by the "Statuto dei lavoratori" have been eliminated by the introduction of an elective model, because this model gives rise to a deep connection between the proportionality principle and the majority principle which may be seen as an instrument of "mediation".