blue law

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A law designed to prohibit or limit the transaction of commercial business or the holding of recreational activities on Sundays.
• noun One of a body of laws in colonial New England designed to enforce certain moral standards and particularly to prohibit specified forms of entertainment or recreation on Sundays.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun law A law that is intended to enforce moral standards.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a statute regulating work on Sundays