In discourse, a heckler's veto is a situation in which a party who disagrees with a speaker's message is able to unilaterally trigger events that result in the speaker being silenced. For example, a heckler can disrupt a speech to the point that the speech is canceled.

In the legal sense, a heckler's veto occurs when the speaker's right is curtailed or restricted by the government in order to prevent a reacting party's behavior. The common example is the termination of a speech or demonstration in the interest of maintaining the public peace based on the anticipated negative reaction of someone opposed to that speech or demonstration.

The term heckler's veto was coined by University of Chicago professor of law Harry Kalven in 1965. Colloquially, the concept is invoked in situations where hecklers or demonstrators silence a speaker without intervention of the law.

In United States case law, the legal underpinning of the heckler's veto is mixed. Most findings say that the acting party's actions cannot be pre-emptively stopped due to fear of heckling by the reacting party, but in the immediate face of violence, authorities can force the acting party to cease their action in order to satisfy the hecklers.

The best known case involving the heckler's veto is probably Feiner v. New York, handed down by the Supreme Court in 1951. Chief Justice Fred M. Vinson, writing for the majority, held that police officers acted within their power in arresting a speaker if the arrest was "motivated solely by a proper concern for the preservation of order and protection of the general welfare". 340 U.S. 315.

In Gregory v. Chicago (1969), Justice Hugo Black, in a concurring opinion, argued that arresting demonstrators as a consequence of unruly behavior of by-standers would amount to a heckler's veto.

In Hill v. Colorado (2000), the Supreme Court ruled that a law which forbade protesters from approaching within eight feet of a person without their consent was not a heckler's veto. Since the protesters could easily convey their message across that gap, the effect of the law was not to prevent speech but to prevent physical harassment. However, the court would not uphold a law which "allowed a single, private actor to unilaterally silence a speaker even as to willing listeners". For example, in Schenck v. Pro-Choice Network of Western New York (1997) it struck down a provision which would require anti-abortion protesters "either to stop talking or to get off the sidewalk whenever a patient came within 15 feet".

University of California, Irvine Law School Dean Erwin Chemerinsky invoked the concept in an editorial following a protest in 2010, in which students disrupted a speech by the Israeli ambassador Michael Oren. Chemerinsky explained that broad freedom exists to invite speakers and hold demonstrations, but that once a speaker has begun an invited lecture,