Is Spam Ordinary Commercial Speech?
http://www.iabc.com/cwb/archive/2004/0304/speech.htm

Morris, Stan
Communication World Bulletin
2004

Abstract:

An informal poll within the U.S. indicates that more than half of respondents favor a law restricting "spam," that is, unwanted electronic advertising that everyone with an e-mail address has been exposed to but does not know how to stop. In the poll, 30 percent favor making false e-mail headers illegal, but only slightly more than 11 percent said spam restrictions would violate the First Amendment.