(CNN) Four UPS employees were arrested in a drug smuggling bust that included the seizure of more than 50,000 counterfeit THC vape pens, authorities said.

Tucson police Sgt. Wally Kaderly told CNN that the employees were arrested November 13 when the first search warrant was executed. Seven other men, not employed by UPS, were arrested in connection with the case, Kaderly said.

The operation included the trafficking of high-grade marijuana, Kaderly said, though he would not provide details beyond saying drug organizations were moving narcotics out of Arizona.

The investigation began in 2017 after police say they discovered evidence of drug trafficking allegedly stemming from UPS employees. The employees arrested include Mario Barcelo, a supervisor who was the focus of the investigation; Gary Love, also a supervisor; and drivers Michael Castro and Thomas Mendoza, Kaderly said.

They face money laundering, drug possession and drug distribution charges, the Washington Post reported. The seven others face charges "related to the shipping of the drugs and operating stash houses for the illicit materials," the newspaper said.

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