PORTLAND, Ore. (KOIN) – Four men are facing charges for drug trafficking in the Portland metro area after authorities found millions of dollars-worth of fentanyl during an operation, Acting U.S. Attorney Scott Erik Asphaug of the District of Oregon announced Thursday.

During the operation on Tuesday, authorities seized 150,000 counterfeit prescription pills that contained fentanyl, and 20 pounds of suspected bulk fentanyl, all worth about $4 million, officials said.

Authorities led the operation after learning 27-year-old Ufrano Orozco Munoz allegedly conspired with others to traffic large amounts of fentanyl from Mexico to the Portland area.

29-year-old Abraham Vera Enriquez, 36-year-old Jesus Miguel Zamora Cruz and 32-year-old Jose Javier Valdez Paramo, who all worked with Orozco, were also arrested.

The men were charged with conspiring to possess with intent to distribute fentanyl.

Homeland Security Investigations started investigating Orozco last month for his role in trafficking fentanyl from Mexico to distribute in western states including Oregon and Arizona.