Organizations today are required to adhere to a number of compliance concerns from laws, regulations and policies. Compliance is achieved through defining and implementing so-called controls in the organizations' business processes. Organizations that build their systems based on the process-driven SOA paradigm realize business processes through orchestration of services to handle the different process activities. We propose an approach for monitoring compliance in SOA systems - we represent a service invocation as an event, enabling us to map business process activities into trails of events that make up compliant processes. The event trails guide the creation of rules, which are leveraged by complex event processing techniques to monitor processes for compliance. A case study from the telecommunications sector demonstrates how we achieve compliance detection. In this case study, we use our approach to identify violations of licensing compliance requirements in the business process of a multimedia service provider.