Actually, the federal Fair Labor Standards Act (FLSA) in 1938 established the 40 hours at straight time week and required time and a half for all hours actually worked over 40 hours.   It does not establish the 5 day standard, and M - F, 8 hours a day is by no means standard.   If you work in retail, you're lucky to get a weekend off once a month or so.  Some states, two or three last I looked, require overtime for work over eight hours in a day.   The unions make the claim that the "gave us the weekend," but in the industries that were heavily unionized at the time of the FLSA, passage, manufacturing, construction, mining, transportation, 24/7 operations were very common and weekends off were rare.