an agency’s discretionary order be upheld, if at all, on the same basis articulated in the order by the agency itself:
“[A] simple but fundamental rule of administrative law . . . is . . . that a reviewing court, in dealing with a determination or judgment which an administrative agency alone is authorized to make, must judge the propriety of such action solely by the grounds invoked by the agency. If those grounds are inadequate or improper, the court is powerless to affirm the administrative action . . . .” Ibid.
For the courts to substitute their or counsel’s discretion for that of the Commission is incompatible with the orderly functioning of the process of judicial review. This is not to deprecate, but to vindicate (see Phelps Dodge Corp. v. Labor Board, 313 U. S. 177, 197), the administrative process, for the purpose of the rule is to avoid “propel [ling] the court into the domain which Congress has set aside exclusively for the administrative agency.” 332 U. S., at 196.
The second and longer answer to the attempted justification is that there is not substantial evidence of record upon which to base a finding that a cease-and-desist order would have been ineffective. There was every indication at the time that a cease-and-desist order would render the deficiencies in service purely temporary phenomena and would thus be effective in promoting adequate, economical, and efficient service and in fostering sound economic conditions among the carriers affected.
It is said that attempted compliance by the unionized carriers might in some way “so aggravate their labor difficulties as to cause a complete cessation of operations.” But this ignores the Commission’s conclusion that carrier apprehensions of teamster reprisals were exaggerated and unwarranted. It further ignores the fact that, as the Commission was aware, the National Labor Relations Board