In this paper we propose an access control model for use by a trusted middleware infrastructure, which is part of an architecture that supports the operation of Location Based Services (LBSs) over the Internet. This access control model provides users with increased security, and particularly privacy, by enabling them to create two different types of permissions based on how their location information is being used. These permissions specify which users and LBSs are entitled to obtain location information about which other users, under what circumstances the location information is released to the users and LBSs, and the accuracy of any location information that is released to the users and LBSs.