The US Justice Department filed criminal charges against four Chinese chemical companies and eight Chinese nationals on Friday, accusing them of trafficking fentanyl precursor chemicals to the Sinaloa cartel. Two high-ranking employees at the Chinese company, Amarvel Biotech, were arrested in Hawaii. The indictments mark the first time that Chinese producers, rather than cartel members, are being prosecuted for their alleged role in the US fentanyl epidemic.

Fentanyl is the leading cause of death for Americans under 50, responsible for 110,000 overdoses in 2022. The escalating death toll is pushing Washington to crack down on the foreign and domestic forces responsible for the drug crisis.

Fentanyl has been coming to the US from China since 2013. After the US pressured China to regulate the drug in 2019, manufacturers shifted to producing its raw materials, chemically camouflaging them for shipment, and giving cartels the scientific know-how to manufacture it in their own laboratories.

The crackdown on China’s fentanyl traffickers comes amid increasingly strained tensions between the two countries. China stopped cooperating with US counter-narcotic efforts after Nancy Pelosi visited Taiwan last year, but it agreed to participate in a joint effort to clamp down on precursor chemicals during Secretary of State Anthony Blinken’s visit to Beijing last week– one of the few areas of progress to come from the visit.

But any joint efforts appear unlikely in the wake of the indictments. Beijing has “strongly condemned” the charges, accusing the US of unlawfully arresting Chinese nationals and using China as a scapegoat for its drug crisis.