1920 cabotage rule named for a senator

This clue leads to Jones Act. The sections below explain what it refers to, why it matches the clue, and why it may be appearing in the current trend cycle.

The Merchant Marine Act of 1920 is a United States federal statute that provides for the promotion and maintenance of the American merchant marine. Among other purposes, the law regulates maritime commerce in U.S. waters and between U.S. ports. Section 27 of the Merchant Marine Act is known as the Jones Act and deals with cabotage. It requires that all goods transported by water between U.S. ports be carried on ships that have been constructed in the United States and that fly the U.S. flag, are owned by U.S. citizens, and are crewed by U.S. citizens and U.S. permanent residents. The act was introduced by Senator Wesley Jones. The law also defines certain seaman's rights.

Background summary sourced from Wikipedia (CC BY-SA). View source

The Jones Act is the common name for Section 27 of the 1920 Merchant Marine Act, introduced by Senator Wesley Jones; it mandates that domestic waterborne cargo move only on vessels constructed, flagged, owned, and crewed by Americans.