If you'd like to bring pro-union propaganda to the table, I'll have to bring in some Scholarship and point out that the story was complex and as such more unions may not necessarily be a panacea: While unions did play a role in shortening the American work week to 40 hours, broader forces in the labor market played substantial roles as well, like a rapidly expanding economy, reduced immigration, and electrification. I will refer you to The Shortening of the American Work Week: An Economic and Historical Analysis of Its Context, Causes, and Consequences (Whaples, 1991). http://www.jstor.org/stable/2122588

"The eight-hour day was won during this decade primarily through labor market tightness (wage increases, manufacturing employment expansion, and curtailment of immigration)."