The vast majority of organizations - public and private - do not have a written policy with regard to conducting interviews. Consider the potential downstream consequences for the interviewee - reprimand, dismissal, financial penalties, criminal charges, imprisonment, etc. Consider the potential downstream consequences for the interviewer - reprimand, dismissal, civil suit (for public and private personnel) and even criminal charges.
Think about it this way: How can an organization have an ethical standard for conducting interviews without a formalized, written interviewing policy?
With the potential for such a vast array of problems associated the conduct of the interview, why do you think so many organizations choose not to address the issue?