Another legal battle between two mobile companies is starting to heat up.

Apple today said that it’s suing Qualcomm for $1 billion. The Cupertino company claims that Qualcomm has used its position as a maker of important cellphone chips to ask for “onerous, unreasonable and costly” patent licensing terms.

Here’s Apple’s statement on its lawsuit with Qualcomm:

“We are extremely disappointed in the way Qualcomm is conducting its business with us and unfortunately after years of disagreement over what constitutes a fair and reasonable royalty we have no choice left but to turn to the courts.”

In its complaint against Qualcomm, Apple also says that Qualcomm recently began withholding rebates owed to Apple. A deal between the companies required Apple to give Qualcomm a part of the average selling price of the iPhone and to exclusively use Qualcomm chips from 2011 to 2016. Apple would then get a quarterly rebate from Qualcomm.

However, Apple claims that Qualcomm began withholding those rebates in 2016 after Apple met with the Korea Fair Trade Commission. The Korean regulators recently announced that it was fining Qualcomm $853 million for alleged anticompetitive patent licensing practices. Apple says that Qualcomm withheld $1 billion in rebates for meeting with the Korean agency and that Qualcomm tried to get Apple to change its responses and give false info in exchange for those rebates.

Apple’s lawsuit comes just days after the US Federal Trade Commission sued Qualcomm for allegedly using unlawful tactics to retain a monopoly in the supply of a semiconductor used in cellphones.