This is a lot like asking for a law authorizing anything. Laws and private property rules generally state what is
not acceptable - seldom give permission.
The absence of law/rule against something, makes it ex post facto legal.
See this however:
Policy is to follow the law of the state the store located.
Customer Service1-800-Wal-Mart
(1-800-925-6278) Questions regarding a
Wal-Mart Store issue
702 SW 8th Street
Wal-Mart Stores, Inc.
Bentonville, Arkansas 72716-8611
Email contact link:
http://walmartstores.com/contactus/feedback.aspx
If you still need/want someting for your personal file, make the contact and post it here. As for me, Walmart is a shining example of how a smart merchant handles this.