BLOW THE WHISTLE ON

{v. phr.}, {slang} 1. To inform against; betray. * /The police caught one of the bank robbers, and he blew the whistle on two more./ 2. To act against, stop, or tell people the secrets of (crime or lawlessness). * /The mayor blew the whistle on gambling./ * /The police blew the whistle on hot reading./