I don't know if anyone has read Oil! by Upton Sinclair. It was radically reworked as "There Will Be Blood" in 2007 and starred Daniel Day-Lewis. The book (rather than the film) focused on the rich/poor unionised dynamic of the West Coast Oil industry.
This book, despite it having a sprinkling of race involvement, looks at the rich/poor dynamics of the Boston Police Force (policemen were hideously treated in 1918 and we get the build up to the Boston PD strike here). Consequently it reminded me strongly of Oil!
I'm not sure what to think of this book. It's long, granted, and I'm not sure what the point of it was given how much it reminded me of Oil!, but it's interesting and will open your eyes to what happened to the left (and race politics) in America at the time.