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 Missouri, as in all states, the First Amendment to the United States Constitution protects individuals from government actions that would abridge their freedom of speech. This protection does not extend to private entities, meaning that private businesses and individuals are not generally restricted by the First Amendment from limiting speech on their property or platforms. However, when it comes to commercial speech, which includes advertising and other speech proposing a commercial transaction, there is still some level of First Amendment protection, albeit less than that afforded to 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 regulation. This test is used to ensure that any government regulation of commercial speech in Missouri is justified by a substantial interest, directly advances that interest, and is not more extensive than necessary. An attorney advising on matters of free speech in Missouri would consider both federal constitutional principles and any relevant state statutes that may offer additional protections or regulations concerning speech.