Regulated parties frequently act on agency guidance that does not have the force of law, and the protection it provides varies considerably.

Formal interpretive rules and official interpretations issued through prescribed processes may provide a statutory safe harbor, and in some statutes good faith conformity with an official interpretation is a complete defense even if it is later amended or determined to be invalid.

Advisory opinions and interpretive letters issued to a specific requester bind the agency as to that requester on the stated facts, and are persuasive elsewhere.

No-action letters state that the staff will not recommend enforcement. They bind the staff and not the agency or private litigants.

Frequently asked questions, bulletins and speeches are not binding on anyone, may be withdrawn without process, and cannot create obligations. Agencies have been criticized for using them as de facto rules, and they cannot be enforced as if they were.

Reliance value. Documented reliance on guidance is evidence of good faith bearing on penalties and on scienter, even where it is not a defense to liability.

Practical guidance. Record the guidance relied on, its date and version, and the analysis, in a contemporaneous memorandum. Guidance changes, and the file is the only evidence of what was reasonable at the time.