In this paper we consider the situation where a set of enterprises need to collaborate to provide rich services to their clients. Such collaboration often requires controlled access to each other's data, which we assume is stored in standard relational form. The access control is provided by a set of access rules that may be defined over the joins of various relations. In this paper we introduce the notion of consistency of access rules and devise an algorithm to ensure consistency. We also consider the possibility of occasional changes in access rules and address the problem of maintaining consistency in the face of such changes. We propose algorithms for both changes with new privileges grants and revocations on existing privileges.