1
general::
Warn or reprimand forcefully or severely, as in When he was caught throwing stones at the windows, the principal read him the riot act. This term alludes to an actual British law, the Riot Act of 1714, which required reading a proclamation so as to disperse a crowd; those who did not obey within an hour were guilty of a felony. [First half of 1800s]
American Heritage Idioms
2
general::
Phrase(s): read someone the riot act
Fig. to give someone a severe scolding. • The manager read me the riot act for coming in late. • The teacher read the students the riot act for their failure to do their assignments.
McGrawhill's American Idioms And Phrasal Verbs