Postal Reorganization Act

The Postal Reorganization Act of 1970 was a law passed by the United States Congress that abolished the then United States Post Office Department, which was a part of the cabinet, and created the United States Postal Service, a corporation-like independent agency with an official monopoly on the delivery of mail in the United States. Pub.L. 91–375 was signed into law by President Richard Nixon on August 12, 1970.

The legislation was a direct outcome of the U.S. postal strike of 1970.

The first paragraph of the Act reads:

The Postal Reorganization Act (at 39 U.S.C. § 410(c)(2)) exempts the USPS from Freedom of Information Act (FOIA) disclosure of "information of a commercial nature, including trade secrets, whether or not obtained from a person outside the Postal Service, which under good business practice would not be publicly disclosed".

...
Wikipedia