The source of authority for an engagement supervisor to make contact with external parties, such as obtaining maintenance reports from a contractor, typically comes from the provisions outlined in the internal audit charter. This charter formally defines the purpose, authority, and responsibility of the internal audit activity, including interactions with third-party service providers. It is essential as it sets the audit activity's scope, allowing auditors to access necessary information and resources.References:
* The Institute of Internal Auditors (IIA) - International Professional Practices Framework (IPPF), specifically the Audit Charter guidelines.