Upton Sinclair's famous novel The Jungle resulted in the passing of the Meat Inspection Act of 1906.
This book by Sinclair was technically fiction but it did give an accurate description of working conditions in the meat packing industry. By following the fictious story of an immigrant, Sinclair painted the scence for American citizens by describing the unsanitary practices used by the meat packing industry. The book exposed this industry for disgusting practices, like including rats in their processed meat.
This book outraged American citizens and the government. This is why Teddy Roosevelt helped to pass the Meat Inspection Act of 1906. The law resulted in the federal regulation of this industry to ensure the meat being sold to the American public was sanitary and not tainted.