Apple’s antitrust trial against Qualcomm has shined a light on the companies’ long-standing partnership that reached a boiling point in 2017. After Apple sued the chipmaker in 2017, Qualcomm refused to provide cellular modems for Apple’s 2018 iPhone lineup, Apple Chief Operating Officer Jeff Williams testified Monday to the Federal Trade Commission, Bloomberg reports.

Apple alleges Qualcomm’s refusal to negotiate in good faith forced it to exclusively use Intel chips in the iPhone XS, iPhone XS Max and the iPhone XR. At issue are Qualcomm’s licensing practices and fees. Apple accuses the company of charging high royalty rates and refusing to license patents to other chipmakers, which contributed to a monopoly for Qualcomm.