From the business.gov web site:
Online Advertising Law
An old cartoon in the New Yorker showed two dogs in front of a computer, and had the caption “On the Internet, Nobody Knows You’re a Dog.” The inherent anonymity of the Internet has fostered a number of shady advertising and marketing practices, such as unsolicited e-mail spam. Over the past decade, federal and state governments have passed additional advertising laws that protect consumer privacy and ensure fair and truthful advertising practices online. If you plan to advertise online — whether you’re buying ads on search engines or direct marketing through e-mail — you’ll need to understand some basic rules.
- Advertising and Marketing on the Internet : Rules of the Road
Discusses the applicability of federal advertising laws to Internet advertising and marketing. - Dot Com Disclosures : Information about Online Advertising
This fact sheet describes information businesses should consider as they develop online ads to ensure that they comply with the law. - CAN-SPAM Act : Requirements for Businesses
The CAN-SPAM Act of 2003 (Controlling the Assault of Non-Solicited Pornography and Marketing Act) establishes requirements for those who send commercial email, spells out penalties for spammers and companies whose products are advertised in spam if they violate the law, and gives consumers the right to ask emailers to stop spamming them. Commercial e-mail messages must include notice that the message is an advertisement or solicitation, an opt-out notice, and a valid postal address of the sender. CAN-SPAM also prohibits falsification of transmission information and deceptive subject headings. The Act creates criminal prohibitions against those who knowingly transmit spam through others’ computers without authorization. Also, the Federal Trade Commission may pursue individuals who knowingly hire others to send deceptive spam. - “Remove Me” Responses and Responsibilities
Claims that you make in any advertisement for your products or services, including those sent by email, must be truthful. This means that you must honor any promises you make to remove consumers from email mailing lists