blow the whistle (on) (someone), to

blow the whistle

 (on someone)
1. Fig. to report someone's wrongdoing to someone (such as the police) who can stop the wrongdoing. (Alludes to blowing a whistle to attract the police.) The citizens' group blew the whistle on the street gangs by calling the police. The gangs were getting very bad. It was definitely time to blow the whistle.
2. Fig. to report legal or regulatory wrongdoing of a company, especially one's employer, to authorities. She was fired for blowing the whistle on the bank's mismanagement of accounts, but she then sued the bank.
See also: blow, whistle

blow the ˈwhistle (on somebody/something)

(informal) stop somebody doing something illegal or wrong by telling a person in authority about it: One of the police officers blew the whistle on his colleagues when he found out they were taking bribes. ▶ ˈwhistle-blower noun a person who informs people in authority or the public that the company they work for is doing something wrong or illegal: The company has denied a whistle-blower’s allegations of poor security.
This idiom probably comes from football, where a referee blows a whistle to stop the game when a player breaks the rules.
See also: blow, whistle

blow the whistle

Slang
To expose a wrongdoing in the hope of bringing it to a halt: an attorney who blew the whistle on governmental corruption.
See also: blow, whistle

blow the whistle (on) (someone), to

To give away, to betray. This expression originally (late nineteenth century) meant ending something suddenly, as though by the blast of a whistle, but by the 1930s it had its present meaning. “Now that the whistle had been blown on his speech,” wrote P. G. Wodehouse in 1934 (Right Ho, Jeeves).
See also: blow, whistle