Secure workflow management systems (WfMSs) are required to support major security features such as authentication, confidentiality, data integrity, and nonrepudiation. The Chinese wall security model (CWSM) was designed to provide access controls that mitigate conflict of interest in commercial organizations, and is especially important for large-scale interenterprise workflow applications. This paper describes how to implement the CWSM in a WfMS. We first demonstrate situations in which an access control model is not sufficient for this if the WfMS does not keep the run-time history of data accesses and company information is mutable, and we then propose an application programming interface (API) to solve this problem, also providing support for the intrinsic dynamic access control mechanism defined in the CWSM (i.e., the dynamic binding of subjects and elements in the company data set). This API can also specify several requirements of the dynamic security policy that arise when applying the CWSM in WfMSs. Finally we discuss how to implement a run-time system to implement CWSM policies specified by this API in a WfMS.