Final answer:
The American Counseling Association (ACA) Code of Ethics explicitly prohibits sexual relationships between a counselor and a client, as they can be exploitative and harmful.
Step-by-step explanation:
The question addresses the Code of Ethics for counselors outlined by the American Counseling Association (ACA). The specific subject in question is the prohibition of certain dual relationships that could impair the counsellor's objectivity, potentially harm the client, and violate professional boundaries. The ACA explicitly prohibits sexual relationships between a counselor and a client because they can be exploitative and damaging to the client's well-being. This ethical stance is grounded in the principle of nonmaleficence, which is central to the counseling profession and is aimed at preventing harm to clients.