Labor spying in the United States has involved people recruited or employed for the purpose of gathering intelligence, committing sabotage, sowing dissent, or engaging in other similar activities, in the context of an employer/labor organization relationship. Spying by companies on union activities has been illegal in the United States since the National Labor Relations Act of 1935.
Statistics suggest that, historically, trade unions have been frequent targets of labor spying. Labor spying is most typically used by companies or their agents, and such activity often complements union busting. In at least one case, an employer hired labor spies to spy not only upon strikers, but also upon strikebreakers that he had hired.
Sidney Howard observed in 1921 that the labor spy, "often unknown to the very employer who retains him through his agency, is in a position of immense strength. There is no power to hold him to truth-telling." Because the labor spy operates in secret, "all [co-workers] are suspected, and intense bitterness is aroused against employers, the innocent and the guilty alike."
Historically, one of the most incriminating indictments of the labor spy business may have been the testimony of Albert Balanow (some sources list the name as Ballin or Blanow) during an investigation of the detective agencies' roles during the Red Scare. Albert Balanow had worked with both the Burns Detective Agency and the Thiel Detective Agency. Balanow testified that the Red Scare was all about shaking down businessmen for protection money. "If there is no conspiracy, you've got to make a conspiracy in order to hold your job."
The sudden exposure of labor spies has driven workers "to violence and unreason", including at least one shooting war.
Labor spies are usually agents employed by corporations, or hired through the services of union busting agencies, for the purpose of monitoring, disempowering, subverting, or destroying labor unions, or undermining actions taken by those unions.