blue law 
noun North American
1A law prohibiting certain activities, such as shopping, on a Sunday.My friend points me to the following article about how the state may relax its blue laws and allow cities to permit selling alcohol on Sundays....
- Not surprisingly, many critics chafed at this populist behavior and attempted to regulate it through a variety of blue laws, fees, and restrictions.
- Shorter workdays became more important than rest on Sunday, and American courts and society found practically any commercial activity to be a necessity and thus exempt from blue laws.
1.1(In colonial New England) a strict puritanical law, particularly one preventing entertainment or leisure activities on a Sunday.The club was one of the many after-hours drinking clubs that dotted the streets of Philadelphia in the days when the old blue laws were still on the books....
- He says ‘yes,’ but Massachusetts' Attorney General says no - and is enforcing his state's old blue law against the markets.
- The blue laws of New England forbade the playing of cards and other common games on the Sabbath.