Blue Laws are (well, actually mostly now) were laws that restricted what products and services could be legally traded on Sundays over much of the United States. They varied from region to region, with some places pretty much shutting down everything except emergency medical treatment, to other places where there was little difference from other days.
In most of the United States, Blue Laws no longer exist for the most, except for the sale of alcohol, and they are vestigial remnants in that area. When I was a child (only months after the last mass extinction that killed the dinosaurs, LOL!), Blue Laws were common in west central Arkansas, and applied to lots more than alcohol.