Hunt- I believe there were state level cases which address the issue you raise in NY back in the 1970’s. Retailers commonly refused to accommodate sabbath observers, until a court pointed out that if a company opens its stores every day of the week (and gives employees two days off), refusing to hire Seventh Day Adventists or observant Jews or Muslims was a very odd (and ultimately- illegal) practice.
I don’t have a citation- sorry- and it’s ancient history.