In the United States, censorship involves the suppression of speech or public communication and raises issues of freedom of speech, which is protected by the First Amendment to the United States Constitution. Interpretation of this fundamental freedom has varied since its enshrinement. Traditionally, the First Amendment was regarded as applying only to the Federal government, leaving the states and local communities free to censor or not. As the applicability of states rights in lawmaking vis-a-vis citizens' national rights began to wane in the wake of the Civil War, censorship by any level of government eventually came under scrutiny, but not without resistance. For example, in recent decades, censorial restraints increased during the 1950s period of widespread anti-communist sentiment, as exemplified by the hearings of the House Committee on Un-American Activities. In Miller v. California (1973), the U.S. Supreme Court found that the First Amendment's freedom of speech does not apply to obscenity, which can, therefore, be censored. While certain forms of hate speech are legal so long as they do not turn to action or incite others to commit illegal acts, more severe forms have led to people or groups (such as the Ku Klux Klan) being denied marching permits or the Westboro Baptist Church being sued, although the initial adverse ruling against the latter was later overturned on appeal to the U.S. Supreme Court case Snyder v. Phelps.
The First Amendment protects against censorship imposed by law, but does not protect against corporate censorship, the restraint of speech of spokespersons, employees, or business associates by threatening monetary loss, loss of employment, or loss of access to the marketplace. Legal expenses can be a significant hidden restraint where there is fear of suit for libel. Many people in the United States are in favor of restricting censorship by corporations, citing a slippery slope that if corporations do not follow the Bill of Rights, the government will be influenced.