The letter calls on executives to review ethics and transparency at the company.
The letter’s contents were confirmed by a Google employee who helped organize it but who requested anonymity because of the sensitive nature of the debate.
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The letter says employees lack the information required “to make ethically informed decisions about our work” and complains that most employees only found out about the project — nicknamed Dragonfly — through media reports.
The letter is similar to one thousands of employees had signed in protest of Project Maven, a U.S. military contract that Google decided in June not to renew.