China International Marine Containers (CIMC), the world largest box maker, has launched lawsuits against several of China Cosco Shipping’s container units in a rare spat between Chinese state-owned conglomerates.

The patent suits have come after Cosco Shipping agreed to take over Singamas’s dry box manufacturing business units—the world’s second largest—for CNY 3.8bn ($565m) earlier this week.

According to some Chinese media outlets, CIMC has filed a petition to Qingdao Intermediate People’s Court accusing two Singamas units being sold to Cosco Shipping of manufacturing and selling containers in violation of its patent, while asking for compensations totalling CMY 1bn.