Chinese smartphone maker Coolpad Group said its unit has sued three group firms of Xiaomi, which last week filed for a Hong Kong IPO that could be worth up to $10 billion, for patent infringement.

Coolpad said in a statement late on Thursday its subsidiary, Yulong Computer Telecommunication Scientific (Shenzhen) filed a lawsuit against Xiaomi Telecom Technology, Xiaomi Technology and Xiaomi Factory in a court in Jiangsu province for using its patent without authorization.

Yulong demanded that the Xiaomi companies should immediately stop production and sale of some smartphone models, including the Mi MIX2, Coolpad said.

Xiaomi last week filed its IPO plans, which could be the largest listing globally in almost four years.

Coolpad has alleged that Xiaomi violated its patented multi-simcard design and other technology related to user interface. It demanded that Xiaomi compensate it for losses due to the alleged infringement, though Zhang declined to give a figure.

In a statement, Xiaomi said it has requested patent authorities to invalidate patent rights that are the subject of the lawsuit filed in Shenzhen. It said it will fully cooperate in the investigation by authorities on the matter.