read the riot act Definition

historical:
1. An Act passed in 1715 and repealed in 1967, designed to prevent riotous assemblies by making it a felony, after the reading of a section of the act by a magistrate or other authority, for a gathering of more than 12 people to refuse to disperse within an hour.
2. The section of the act read as a warning to rioters to disperse.

jocular
To give an angry warning that bad behaviour must stop.