Endicott Johnson Corp. v. Perkins (317 U.S. 501 (1943)) was a follow up to Crowell
v. Benson (285 U.S. 22 (1932)), and
applied the notion of ultra vires to subpoena powers. In the
case, Johnson resisted a subpoena because they felt that the Administrative
Agency was acting outside their jurisdiction.
The Court found that the
information in the subpoena was necessary for the agency to determine
where their jurisdictional limits were.
Basically, an agency can
conduct an inquiry to determine their jurisdiction, even if it later turns
out that the people getting subpoenaed were outside of the agency's