A Federal Bureau of Prisons employee died after coming into contact with an unknown substance in the mailroom at the U.S. penitentiary in Atwater, California, according to a bureau spokesperson.

       The Bureau of Prisons is investigating whether the employee was exposed to fentanyl, sources told ABC News.

       The employee began to feel unwell on Friday after coming into contact with the substance and was rushed to the hospital where he was pronounced dead, according to the BOP. A second employee came into contact with the substance, was observed at the hospital and released.

       "Our hearts are heavy as we extend our deepest condolences to the family, friends, and colleagues of our fallen Bureau employee," a Bureau of Prisons spokesperson said. "Out of respect for the family's privacy and the grief of our Bureau community, we have no further details to share at this time."

       The Council of Prison Locals, the BOP's largest union that represents employees, has been advocating for more mailroom safety measures, according to Council President Brandy Moore-White.

       A bill was introduced by Rep. Don Bacon, R-Neb., in December 2023 that would require the agency to electronically scan all the mail coming into the facilities. It is unclear what the procedures are now.

       The bill has yet to make it out of the Judiciary Committee.