AU-C Section 200.16: Ethical Requirements

AU-C Section 200.16 says:

"The auditor should comply with relevant ethical requirements relating to financial statement audit engagements."

In acting ethically, the auditor should assume an obligation of self-discipline above and beyond the requirements of laws and regulations.  This includes an unswerving commitment to honorable behavior in dealings with the public, his clients, and his colleagues, even at the sacrifice of personal advantage.  The AICPA Code of Professional Conduct establishes the fundamental principles of professional ethics, which include the following. 

• Responsibilities: The auditor should exercise sensitive professional and moral judgments in all his activities.  This responsibility is to the well-being of all those who use the auditor's professional services and to the art of accounting, the public's confidence, and the profession's special responsibilities of self-governance.
• The Public Interest: The auditor should accept the obligation to act in a way that will serve the public interest, honor the public trust, and demonstrate a commitment to professionalism.  The public interest includes the community of people and institutions that the profession services (e.g., clients, credit grantors, governments, employers, investors, the business and financial community, etc.)
• Integrity: The auditor should perform all professional responsibilities, making decisions according to what is right and just.  This means the auditor must be honest and candid, and should not subordinate his level of service to personal gain and advantage. 
• Objectivity and Independence: The auditor should remain independent in fact and appearance when carrying on his professional services.  This means the auditor must be impartial, intellectually honest, and free from conflicts of interest. 
• Due Care: The auditor should observe the profession's technical and ethical standards, strive continually to improve competence and the quality of services, and discharge professional responsibility to the best of his ability.  The auditor should employ a quest for excellence, through continual improvement in competence, and diligence in discharging his responsibilities to those he serves. 
• Scope and Nature of Services: The services the auditor provides should be in line the Code of Professional Conduct.  This means that the auditor should only practice in firms that have in place appropriate quality control procedures to ensure that services are competently delivered and adequately supervised, only participate in engagements that are free from conflicts of interest, and only take on activities that are consistent with his role as a professional.

Please note the auditor must also follow other ethical requirements promulgated by his regulators (e.g., state boards of accountancy, and other regulatory agencies).  These ethical requirements are typically embodied in the firm's Quality Control Policies, which are explained in detail at AU-C Section 220.

https://www.aicpa.org/content/dam/aicpa/research/standards/auditattest/downloadabledocuments/au-c-00200.pdf

https://pub.aicpa.org/codeofconduct/Handlers/DownloadDocument.ashx?docid=19976&d_ft=2