Answer: The Meat Inspection Act.
The Federal Meat Inspection Act (FMIA) was passed in 1906, and it made it a crime to adulterate or misbrand meat. It also ensured that meat and meat products were slaughtered and processed under sanitary conditions.
The main motivation for this law was to protect the diet and health of the American consumer. This was a response to the book The Jungle by Upton Sinclair, an exposé of the meat packing industry in Chicago.