Apple Inc. has sued Qualcomm Inc. for $1 billion, according to published reports.

Several financial publications said Apple (Nasdaq: AAPL) is seeking $1 billion in rebates that the San Diego chipmaker reportedly promised it. The lawsuit also questions whether Apple should be paying Qualcomm (Nasdaq: QCOM) royalties on certain intellectual property.

Apple filed the lawsuit Jan. 20 in San Diego federal court. The move caps a week when the Federal Trade Commission filed its own lawsuit against Qualcomm, alleging that that the San Diego company violated antitrust law. Qualcomm issued a strongly worded statement saying it planned to fight the FTC.

Qualcomm is also being fined $865 million by South Korean antitrust regulators, and it faces investigations in the European Union and Taiwan. Qualcomm has said it would fight the South Korean fine.

Apple’s reported cooperation with the South Korean antitrust investigation plays into the Silicon Valley company’s new legal battle with Qualcomm, according to Bloomberg News and Forbes.

Qualcomm dismissed Apple's allegations.

“While we are still in the process of reviewing the complaint in detail, it is quite clear that Apple’s claims are baseless,” said Don Rosenberg, Qualcomm’s general counsel, in a statement released late Friday. “Apple has intentionally mischaracterized our agreements and negotiations, as well as the enormity and value of the technology we have invented, contributed and shared with all mobile device makers through our licensing program. Apple has been actively encouraging regulatory attacks on Qualcomm’s business in various jurisdictions around the world, as reflected in the recent [South Korean] decision and FTC complaint, by misrepresenting facts and withholding information. We welcome the opportunity to have these meritless claims heard in court where we will be entitled to full discovery of Apple’s practices and a robust examination of the merits.”

Qualcomm settled an antitrust action with the Chinese government in early 2015 by paying a $975 million fine and changing its royalty terms for Chinese customers.