p Qualcomm’s battle with Apple is heating up as the chip company hauls assemblers of the iPhone into a US court on claims they are failing to pay patent royalties.

Four Asian contract manufacturers, including Foxconn Technology Group and Pegatron, aren’t complying with obligations to pay for the use of patented technology, according to a complaint Qualcomm said it filed in federal court in San Diego.

The other two companies sued are Wistron Corp. and Compal Electronics Inc.

Unlike other smartphone companies, Apple doesn’t have a direct license with Qualcomm and instead pays contractors to make its devices, parts of which are used to cover royalties such as those owed under agreements struck before the first iPhone appeared.

The chipmaker blamed Apple for dragging its contract manufacturers into the dispute, saying the decision not to give them money for royalties had stopped them from paying Qualcomm, according to the complaint.

“Their gripe, their issue, appears to be with Apple,” said Qualcomm General Counsel Don Rosenberg.

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