blow the whistle on

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.
Categories: {slang} {v. phr.}