Agency manuals, guidelines, and memoranda may be construed to be interpretive rules. Legislative rules are those affecting private rights, privileges, or interests in what amounts to a legislative act.
Legislative rules have the force of law.
Interpretive rules, on the other hand, do not create rights but merely clarify an existing statute or regulation. Because they only clarify existing law, interpretive rules need not go through the legislative authorization process. Although they are entitled to some deference from the courts, interpretive rules do not have the force of law nor are they irrevocably binding on the agency or the court. When a rule is legislative, the reviewing court has no authority to substitute its judgment as to the content of the rule, for the legislative body has placed the power in the agency and not in the court. Legislative rules are promulgated pursuant to specific statutory authority provided by the legislature and have the force and effect of law and a presumption of validity attached to them.