HR should be barred to ask candidates CTC because when they mention in the offer letter to keep it confidential. Candidates should take strict action and not to mention their CTC to other company HR
HR functions as any other function which has budget involved in it and taken care of, so it is important for them to have idea about cost of every action. Asking about the CTC from the candidate provides the HR to know about how much cost addition the new candidate be to the total expense