To start I would definitely recommend one of the works that had a major impact on labor. Upton Sinclair's The Jungle. It's a novel not a scholarly work but the allegations made in the work were sufficiently justified that the book directly led to the creation of the FDA. The book gives a good feel for some of the worst conditions for labor during the turn of the century although I warn that it is a bit sensational don't read everything from the book as absolute truth or as the standard at all factories.