Plaintiffs' attorneys said US District Court Judge Lucy Koh endorsed questioning Cook, Schmidt, as well as Intel head Paul Otellini, after reasoning that high-level executives would know about restrictions on hiring talent.

During a hearing Thursday in her courtroom in the California city of San Jose, Koh referred repeatedly to email evidence that included a request in 2007 by then Apple chief Steve Jobs that Google stop recruiting Apple workers.

While Cook was not mentioned in the email messages, it was reasonable to expect that his position as chief operating officer included being kept apprised of issues involving employee expenses, the judge said.