blow the whistle

Meaning

1. (idiomatic, usually) To disclose information to the public or to appropriate authorities concerning the illegal or socially harmful actions of a person or group, especially a corporation or government agency.
2. To make a piercing sound which signals a referee's action or the end of a game.

Synonyms

betray

tell on

Etymology

When used idiomatically, probably an allusion to a police officer blowing his or her whistle on observing a violation of the law.