Chilling effect (law)

A chilling effect is a term in law and communication which describes a situation where speech or conduct is suppressed by fear of penalization at the interests of an individual or group. It may prompt self-censorship and therefore hamper free speech. Since many attacks rely on libel law, the term libel chill is also often used. This is the same concept as a Strategic Lawsuit Against Public Participation, or "SLAPP" suit.

Usage
In United States and Canadian law, the term chilling effects refers to the stifling effect that vague or overbroad laws may have on legitimate speech activity. Recognition of a law that may permit a loophole for such chilling effect as a vehicle for political libel or vexatious litigation provides a prompt to allow changes to such defamation laws, and therefore prevent the suppression of free speech and censorship.

History
The term chilling effect had been in use in the United States since as early as 1950. It, however, became further used as a legal term when William J. Brennan, a justice of the United States Supreme Court, used it in a judicial decision (Lamont v. Postmaster General) which required a postal patron receiving "communist political propaganda" to specifically authorize the delivery.

The Lamont case, however, did not center around a law that explicitly stifles free speech. The "chilling effect" referred to at the time was a "deterrent effect" on freedom of expression — even when there is no law explicitly prohibiting it. However, in general, "chilling effect" is now often used in reference to laws or actions that do not explicitly prohibit legitimate speech, but that impose undue burdens.