The electronic representation of a contract for a business-to-business (B2B) partnership should be such that it can be used by a monitoring service for compliance checking of B2B interactions at runtime, ensuring that the interactions match the rights and obligations that each partner has promised to honor. With this view in mind, the paper develops a model for checking contractual compliance of business interactions. Specifically, the paper develops a novel way of representing contract clauses using business rules, that is specially suited to compliance checking and describes what events need to be captured from the underlying messaging middleware and how they can be processed in a careful manner to evaluate contractual compliance.