The works council defined in this title may be set up in undertakings belonging to an economic and social unit. The agreement defined in article L. 2321-2 is concluded either at the level of one or more undertakings making up the economic and social unit, or at the level of the economic and social unit. In the latter case, the rules governing the validity of the agreement are assessed by taking into account the votes validly cast in all the undertakings.