Authorities are investigating a suspicious envelope sent to the elections office in Yuba County on Wednesday morning that might have contained fentanyl.

The Yuba County Sheriff’s Department will investigate the incident. The envelope was sent to the Yuba County Registrar of Voters headquarters, about 40 miles north of the state Capitol in Sacramento.

The package appeared to come from "a verified agency" and didn't look suspicious at first, but a staff member discovered a powdery substance inside that prompted them to call law enforcement, said Yuba County spokesperson Rachel Abbott. A field test showed the presence of fentanyl, but authorities will conduct further analysis to confirm. Abbott said no one was harmed.

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A slew of suspicious packages, including some laced with fentanyl, were sent to elections facilities in at least five states — including California — last November, prompting evacuations and delaying the counting of ballots in some local races. The FBI and U.S. Postal Inspection Service had to step in to intercept such packages in the mail system. Letters intended for election offices in Sacramento and Los Angeles were among those intercepted.

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A package sent to a rural California elections office has tested positive for fentanyl. (Fox News)

Election officials and workers across the country have increasingly faced threats and harassment since former President Donald Trump and his supporters began spreading false election claims after he lost the 2020 election.

Many election offices across the United States have taken steps to increase the security of their buildings and boost protections for workers. Facing the threats of fentanyl-laced packages, some have started stocking up on naloxone, the antidote to fentanyl.

Yuba County officials said workers undergo training on how to identify and handle suspicious packages.

California Secretary of State Shirley N. Weber said her office has provided safety protocols to local elections offices to increase security.

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"I trust that law enforcement authorities will identify and bring to justice any persons responsible for seeking to intimidate, threaten, or harm election workers," Weber said in a statement.