Digital Rights Management (DRM) allows controlling the access, the use and the diffusion of digital contents produced by the rights holders. With this intention, a right expression language is necessary. The MPEG-21 REL is a standardized language used to express the licenses. In this paper, we propose an improvement of the security policy and expressivity of MPEG-21 REL by introducing concepts based on the Or-BAC (Organization Based Access Control) data model. This improvement will be illustrated by some use cases.