The U.S. Department of Justice is investigating whether big tech firms, including Google, Yahoo (NSDQ: YHOO), and Apple (NSDQ: AAPL) broke antitrust law by possibly colluding on hiring policies, according to a report in the Washington Post. Apparently the companies may have agreed not to actively recruit employees away from each other, although details in the WP story and a follow up one in the NYT are scarce.

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The probe is yet another indication that the renewed enforcement push under way by the Justice Department is having a particularly heavy impact on the tech industry. Two other antitrust inquiries this year have targeted Google (NSDQ: GOOG). One is examining the overlap between members of the boards of Apple and Google, while the second is looking into the company’s settlement with book publishers. Google CEO Eric Schmidt has responded by defending the company’s behavior.