A Georgia election worker was arrested Monday on charges that the United States sent a letter threatening to bomb election workers that he wrote to make it appear as if it came from a voter in the key state in the presidential election.

Federal prosecutors said Nicholas Wimbish, 25, was working as a poll worker at the Jones County Election Office in Gray, Georgia, on Oct. 16 when he got into a verbal altercation with a voter.

The next day, Wimbish mailed a letter to the county elections superintendent that was worded to appear as if it came from the same voter, prosecutors said. The letter complained that Wimbish was a “closeted liberal voter fraud” who had been distracting voters in line to cast their ballots, according to the charging documents.

Authorities said the letter, signed by a “Jones County voter,” said Wimbish and others “should look over their shoulders” and warned that people would “learn a violent lesson about stealing our elections.”

Prosecutors said the letter ended with a handwritten note: “PS boom toy at early voting location, burning cigarettes, be careful.”

Wimbish was charged with mailing a bomb threat, transmitting false information about a bomb threat, sending a threatening letter and making false statements to the FBI, prosecutors said. Wimbish’s attorney could not immediately be identified.

Georgia is one of seven hotly contested states expected to decide the outcome of Tuesday’s presidential election showdown between Republican former President Donald Trump and Democratic Vice President Kamala Harris.

Concerns about possible political violence have led officials to take a variety of measures to bolster security during and after Election Day.