read the riot act give someone a strong warning that they must improve their behaviour.

☞ The Riot Act was passed by the British government in 1715 in the wake of the Jacobite rebellion of that year and was designed to prevent civil disorder. The Act made it a felony for a group of twelve or more people to refuse to disperse after being ordered to do so and having being read a certain part of the Act by a person in authority. It was not repealed until 1967.