An Apple spokeswoman declined to comment. Intel and Adobe also declined to comment. Representatives for the plaintiffs, along with Google, could not immediately be reached.
Tech employees alleged that the conspiracy limited their job mobility and, as a result, kept a lid on salaries. The case, filed in 2011, has been closely watched because of the possibility of big damages being awarded and for the opportunity of a glimpse into the world of some of America's elite tech firms.
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Plaintiffs based their case largely on emails in which Apple's late co-founder, Steve Jobs, former Google Chief Executive Officer Eric Schmidt and some of their rivals hatched plans to avoid poaching each other's prized engineers.
In rejecting the proposed settlement, Koh cited "substantial and compelling evidence" that Jobs "was a, if not the, central figure in the alleged conspiracy." Given the strength of the case against the companies, the plaintiffs should have gotten more money, Koh wrote.
A hearing is scheduled for Sept. 10.
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The case is In Re: High-Tech Employee Antitrust Litigation, U.S. District Court, Northern District of California 11-cv-2509.