Pretty much all of Vonnegut’s stuff is very pro-worker and very anti-capitalist. His novel Jailbird covers a fictionalised version of the Pullman Strike, Player Piano deals with automation and how it can negatively impact the worker, Slaughterhouse-five is (among many, many other things) anti-war. God Bless You, Mr. Rosewater concerns the class system and all its flaws. Hell, he dedicated Hocus Pocus to Debs. Plus, he was a fucking fantastic author to boot.