A non-audit service (NAS) that an auditor/ audit firm cannot provide to an auditee (an audited firm). Specific services other than annual financial statements audit may be blacklisted or prohibited as per regulatory measures, which usually vary across jurisdictions, and may include or exclude assurance, tax, advisory and other services that do not relate to core audit services. This also applies to various services such as risk assessment, performance measurement, management advisory, accounting and review, executive recruitment, legal help and corporate recovery, assurance on an entity’s information system, attestation services for certifying the soundness of internal control systems, financial forecasts, and projections, among others.

A blacklist non-audit service (prohibited non-audit services) is known for short as blacklist NAS.