P's smelter is the only significant source of sulfur oxide pollution in the county. D tried to persuade state officials to issue a plan as required by the Clean Air Act Amendments of 1970. The Montana State Board of Health held a public hearing on Montana's proposed implementation plan. P was present and presented its views on the state's proposed regulation for restricting sulfur oxide emissions. Montana submitted to the EPA an implementation plan, but the provision for control of sulfur oxide emissions was omitted. The state plan then was disapproved by Don May 31, 1972, insofar as it excluded the sulfur oxide emissions provisions. D then proposed a regulation to control the emission of sulfur oxide within the County. It limited emissions to a discharge of 7,040 pounds of sulfur oxides per hour. D also gave notice of intent to hold public hearings on its proposal on a date 30 days after the issuance. This provision of the regulation is said to have been patterned after the sulfur oxide emissions limitation which had been in the state's proposal which was deleted. P demanded an adjudicatory hearing on D's proposed regulation. D stated that the public hearings were to be legislative or informational and not adjudicatory. The hearing would not be conducted in the nature of a trial. Instead, any interested persons or corporations could make a statement and all relevant testimony would be received. The hearing record would remain open until October 7, 1972, for written statements or other submissions. After that, there would be a further hearing to allow further public statements. At the hearing, P stated that it was spending large sums of money on its own initiative in an effort to control sulfur oxide emissions; that it was preparing to restrict them from the current rate of 64,000 pounds per hour to 50,000 pounds per hour. Its position was further expressed that the 7,040 pounds per hour would be technologically and economically unfeasible and would create a significant water pollution problem. P filed this suit seeking injunctive relief against various officials of D. P sought relief against the promulgation of the proposed rule. After the suit was filed, an extensive evidentiary hearing was conducted. The district court then rendered a decision. The trial court invoked 42 U.S.C. § 1857h-(2) authorizing citizen suits to enforce the Act. The trial court also considered the case as one in which P's constitutional rights were in jeopardy and reasoned that the emergency relief was justifiable on this ground. It ruled for P and ordered D to conduct an adjudicatory hearing. D appealed.