Music is protected under copyright law, therefore it is generally illegal to play music publicly without a license to do so. Even when you purchase a record or DVD, you are only granted the authorization for a non-public performance, such as in your home or car. No public performance right is attached to the sale of these products. Therefore, if you play this music in your establishment or at your event, you are required to obtain authorization from the copyright owner (or their representative, i.e. ASCAP, BMI, SESAC).The law as it concerns publically playing music is U.S. Code › Title 17 › Chapter 1 › § 101.
See a copy of it here: https://www.law.cornell.edu/uscode/text/17/101
ASCAP has written an informative pamplet entitled, "ASCAP keeps you in tune with the copyright law," which explains why a license is needed and what an ASCAP license covers.
Copyright and the Public Domain from the Public Domain Information Project:
http://pdinfo.com/copyright-law/copyright-and-public-domain.php