Postal Reorganization Act

The Postal Reorganization Act of 1970 was a law passed by the United States Congress that abolished the then U.S. Post Office Department, which was a part of the Cabinet, and created the U.S. Postal Service, a corporation-like independent agency authorized by the U.S. government as an official service for the delivery of mail in the United States. President Richard Nixon signed the Act in law on August 12, 1970.

Source: Wikipedia — Postal Reorganization Act (CC BY-SA 4.0)