Idiom Definition:
"to lay down the law"
to very strongly tell people what they must do, usually without regard for the opinion or feelings of other people
Synonyms:
appoint, authorize, command, compel, decree, demand, dictate, direct, exact, impose, inflict, insist, instruct, oblige, ordain, order, proclaim, require, rule, set, tell
Literally,
laying down the law. - - - - ->