Apple is suing Qualcomm, Bloomberg reported on Friday.
Apple buys wireless chips from Qualcomm and also pays it licenses to use its wireless patents.
Apple is accusing Qualcomm of withholding $1 billion in rebates under a deal they had struck to keep Qualcomm modems in Apple products, including the iPhone and iPad.
Earlier this week, the FTC accused Qualcomm of monopolistic practices, and directly cited its relationship with Apple.
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