In a draft complaint, the FTC said there have been thousands of complaints related to millions of dollars in unauthorized in-app charges by children on Amazon devices. The agency said Amazon only changed its in-app charging policies last month.
Amazon, which has built a rapidly growing business around its Kindle mobile devices and last month unveiled its own smartphone, said in a letter to the FTC it has already met or exceeded the requirements of Apple's terms.
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"The commission's unwillingness to depart from the precedent it set with Apple despite our very different facts leaves us no choice but to defend our approach in court," Andrew DeVore, an Amazon associate general counsel, said in the July 1 letter.
Purchases of digital goods—from extra game lives to special in-game tools—are key to the success of tech companies' app stores, which in turn drive usage and mobile device sales.
In January, Apple agreed to refund customers at least $32.5 million and change its billing practices to ensure it obtains consent from parents before charging for in-app spending.
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The FTC is pushing Amazon to refund customers, give up any profits from inappropriate activity and to compensate for the FTC's costs.
Many parents who discover the charges and want a refund face "significant hurdles to doing so," the FTC said in a draft of its complaint, adding that the process remains unclear, confusing and without clear instructions for obtaining a refund.