Article I, Section 8, Clause 7:
[The Congress shall have Power . . .] To establish Post Offices and post Roads; . . .
The cases just reviewed involved attempts to close the mails to communication that were deemed to be harmful. A much broader power of exclusion was asserted in the Public Utility Holding Company Act of 1935. 1 To induce compliance with the regulatory requirements of that act, Congress denied the privilege of using the mails for any purpose to holding companies that failed to obey that law, irrespective of the character of the material to be carried. Viewing the matter realistically, the Supreme Court treated this provision as a penalty. Although it held this statute constitutional because the regulations whose infractions were thus penalized were themselves valid, 2 it declared that
Congress may not exercise its control over the mails to enforce a requirement which lies outside its constitutional province. . . . 3