NLRB v. Wyman-Gordon: Employer refused to comply with the order the NLRB established in Excelsior with regard to new elections and issuing the list of employees. - (Plurality) Rule: Agencies cannot engage in "prospective only" policy announcements via adjudication and orders, as the APA requires agencies to engage in substantive rulemaking for policies with prospective effect alone. o The agency cannot replace a statutory scheme with a rule-making procedure of its own design. - Black's Concurrence: Exercise of one power does not exclude the use of another (precedent = rule). - Douglas' Dissent: Excelsior rule was invalid, so this rule is also invalid.