A lithium producer for carmakers including BMW and Tesla is beginning work to assess battery metals projects in Xinjiang, deepening links between electric vehicle supply chains and a region at the heart of human-rights allegations against China.

Ganfeng Lithium, China’s top producer of the material, is partnering through a subsidiary with a state-backed entity to accelerate exploration for and potentially develop lithium, nickel and other critical metal assets in the region. Ganfeng’s Chairman Li Liangbin earlier this year visited Xinjiang — where activists and Western governments say Uyghurs and other Muslim citizens have been subjected to forced labor — to discuss cooperating with the local government on the plans.

Electric vehicle (EV) makers already face criticism over labor concerns and environmental damage tied to the extraction of metals used in their products. The deepening connection between Ganfeng and Xinjiang is set to draw more scrutiny from investors and consumers. Ganfeng said in November it had won a new three-year deal to provide battery-grade lithium hydroxide products to Tesla, and has previously disclosed other contracts with companies including BMW.