Definition of heckler's veto in US English:

heckler's veto

noun

US
  • An act of preventing someone from speaking in a public forum because of concerns that opponents of their views will react in a violent or disruptive manner.

    ‘the law professor argued that authorities must protect speech lest those trying to use the heckler's veto learn that they can silence their opponents by making threats’

Origin

1960s: coined by American legal scholar Harry Kalven ( 1914 – 1974).