This is not backed up by any source I can find. Nearly every source says that the 5 day week was invented by unions in the 1800s, popularized by Henry Ford at the Ford motor company due to measurable improvements to productivity, and made law in the 1930s (in the US) to attempt to counter wide-spread unemployment during the Great Depression. Union pressure is not mentioned anywhere, and honestly doesn't make any sense given that unions were not particularly powerful in those time periods.
Unions were so powerful in the early 1900s that multiple revolutions occurred in part due to their pressure and actions all around the industrialised world. And the fear of strikes led to many reforms and regulations to take talking points off unions (like Bismarck enacting the first welfare state to be a step ahead of social democrats).
Specifically in the US, look at the Coal Wars and the Battle of Blair Mountain in which the US army fought with aircraft and artillery against striking miners.
I understand your point and directly disagree with its main part: the move from a family-run farm to a shift-based employment happened before I was born so I did inherit it but it was in fact piloted, tried on small scale, and organic at first.