Policy enforcement is a mechanism for ensuring that system components follow certain programming practices, comply with specified rules, and meet certain assumptions. Unfortunately,the most common mechanisms used today for policy enforcement are documentation, training, and code reviews. The fundamental problem is that these mechanisms are expensive, time-consuming, and still error-prone. To cope with this problem, in this paper, we present IRC (Implementation Restriction Checker), an extensible framework for automatically enforcing system-wide policies or contracts. The framework is built on top of a platform for aspect-oriented programming at the level of Java bytecode instructions and is available as an Eclipse plug-in as well as a standalone application. It includes a set of directly usable checkers and can be easily extended to implement new ones.