I found this[1] report (PDF) from the DEA:
"Currently, China remains the primary source of fentanyl and fentanyl-related substances trafficked through international mail and express consignment operations environment, as well as the main source for all fentanyl-related substances trafficked into the United States. Seizures of fentanyl sourced from China average less than one kilogram in weight, and often test above 90 percent concentration of pure fentanyl."
Presumably, if the CCP wanted to do so, they could put an end to the groups shipping this deadly substance into the United States.