The First Amendment to the United States Constitution provides that Congress shall make no law abridging (curtailing) the freedom of speech. Thus, free speech is only protected by the U.S. Constitution when it is the government that seeks to limit free speech. The First Amendment is inapplicable when a nongovernmental person or entity—such as a private business—seeks to limit free speech.

And some types of speech are afforded more protection than others. For example, commercial speech—speech that proposes a commercial transaction—is entitled to First Amendment protection, but less protection than political speech.

In the 1980 case Central Hudson Gas & Electric Corp. v. Public Service Commission, the U.S. Supreme Court developed a four-part test to determine whether commercial speech regulation violates the First Amendment:

1. Whether the commercial speech concerns a lawful activity and is not misleading;

2. Whether the government interest asserted to justify the regulation is "substantial";

3. Whether the regulation "directly advances" that government interest;

4. Whether the regulation is no more extensive than necessary to serve that interest.

In New Hampshire, as in all states, the First Amendment to the United States Constitution protects individuals from government restrictions on free speech. This means that the state and federal government cannot curtail speech unless it falls under certain exceptions. However, the First Amendment does not apply to private entities, such as businesses, which means they may set their own rules regarding speech on their property or within their organizations. When it comes to commercial speech, which includes advertising or other speech proposing a commercial transaction, it is protected by the First Amendment but to a lesser degree than political speech. The Central Hudson Gas & Electric Corp. v. Public Service Commission case established a four-part test to assess the constitutionality of commercial speech regulations. This test is used to ensure that any restrictions on commercial speech in New Hampshire are justified by a substantial government interest, directly advance that interest, and are not more extensive than necessary.