Qualcomm on Wednesday sued the manufacturers that make iPhones for Apple for failing to pay royalties on the chip maker's technology, widening its legal battle with the world's most valuable company. Qualcomm's lawsuit, filed Wednesday in a federal district court in San Diego, accuses Compal, Foxconn, Pegatron, and Wistron of breaching longstanding patent-licensing agreements with Qualcomm by halting royalty payments on Qualcomm technology used in iPhones and iPads. From a report: Apple sued Qualcomm in January, accusing it of overcharging for chips and refusing to pay some $1 billion in promised rebates. Qualcomm said in the complaint that Apple is trying to force the company to agree to a "unreasonable demand for a below-market direct license." Qualcomm said last month that Apple had decided to withhold royalty payments to its contract manufacturers that are owed to the chipmaker, for sales made in the first quarter of 2017, until the dispute is resolved in court. "While not disputing their contractual obligations to pay for the use of Qualcomm's inventions, the manufacturers say they must follow Apple's instructions not to pay," Qualcomm said in a statement on Wednesday.