Business Process Compliance (BPC) has gained significant momentum in research and practice during the last years. Although many approaches address BPC, they mostly assume the existence of some kind of unified base of process constraints and focus on their verification over the business processes. However, it remains unclear how such an integrated process constraint base can be built up, particularly at the presence of process constraints stemming from heterogeneous sources such as internal controls, external contracts, or security and privacy policies. Hence in this paper, we propose a representation framework for the integration of process constraints stemming from different sources. The representation framework is generic such that existing formalisms to represent process constraints can be integrated. The framework is illustrated by means of real-world process constraints from different domains and heterogeneous sources. Altogether process constraint integration enables consistency checks and optimizations as well as maintenance and evolution of the constraint base.