The Jungle by Upton Sinclair

Sinclair's masterpiece. According to Wikipedia: "Upton Beall Sinclair, Jr. (1878 - 1968), was a prolific American author who wrote over 90 books in many genres and was widely considered to be one of the best investigators advocating socialist views. He achieved considerable popularity in the first half of the 20th century. He gained particular fame for his 1906 novel The Jungle, which dealt with conditions in the U.S. meat packing industry and caused a public uproar that partly contributed to the passage of the Pure Food and Drug Act and the Meat Inspection Act in 1906."