In multicast communications, where service providers distribute sensitive information such as military operations information, an important issue is to control operation participants' access to transmitted data and network resources. This issue becomes more complicated when multicast communications take place in mobile ad hoc network (MANET) environments. In this study, we discuss the multicast security issues in MANET and propose a new approach for securing the communications under these conditions. Specifically, we determine the security requirements based on certain use case scenarios and define access control policies in mobile ad hoc multicast communications accordingly. The goal is to create a new protocol for multicast data dissemination while enforcing the required data access policies. The protocol that we propose is based on the multicast features of the well-known Ad hoc On-Demand Distance Vector Routing (MAODV) protocol and incorporates the features of the role-based access control model. The study shows that our approach is simple, but yet flexible and effective in controlling the access to data being transmitted within the multicast groups.