The emails came from an address that appeared to be affiliated with a far-right group, though an analyst who reviewed one email obtained by CNN said it had been sent using foreign internet infrastructure.
The identity of the person or group behind the messages was unknown, said TJ Pyche, a spokesperson for the Alachua County Supervisor of Elections in Florida.
Pyche said his office "got flooded with phone calls and emails" from dozens of voters about the messages Tuesday and immediately reached out to local, state and federal law enforcement, including the FBI.
University of Florida spokesperson Steve Orlando said 183 people, including students, staff and alumni, received the emails.
The Lawyers' Committee for Civil Rights Under Law received about three dozen reports of voters getting similar email messages Tuesday and at least one of those was from Arizona, said Kristen Clarke, president and executive director of the organization. "Regardless of who is behind this effort it seems the goal is to discourage people from freely casting their ballots," Clarke said.
A spokesperson for the Alaska Division of Elections, Tiffany Montemayor, said the state is aware of Alaskans receiving similar emails and said, "We've forwarded that information to the appropriate federal agencies for their review."
The FBI did not respond to a request for comment.
A spokesperson for the Cybersecurity and Infrastructure Security Agency said in a statement that it is aware of the emails.
"While we are looking into the emails, we can tell you this: your vote IS secret," the spokesperson said. "These emails are meant to intimidate and undermine American voters' confidence in our elections. Don't fall for sensational and unverified claims. Visit CISA.gov/rumorcontrol to get more facts about elections and election security. #Protect2020"
Roxanne Palmer -- a resident of Alachua County, Florida, who is a Democrat -- said she found one of the emails in her spam folder.
The email was sent from "info@officialproudboys.com" and demanded that she vote for Trump "or we will come after you," according to a copy she forwarded to CNN.
"I'm not worried about it," said Palmer, who said she interpreted the message to more likely be a scam or stunt than an actual threat. "I'm sure it's just someone taking advantage of a lot of the fear and tension."
Enrique Tarrio, the chairman of the Proud Boys, said the email "is definitely not" from the Proud Boys.
"We have spoken to the FBI and are working with them. I hope whoever did this is arrested for voter intimidation and for maliciously impersonating our group," Tarrio said.
Tarrio said the website Officialproudboys.com is one of their official websites but it has not been updated for weeks and is down because they have migrated to another website.
"We don't send emails. This is someone spoofing our emails and website," Tarrio told CNN.
Lt. Becky Butscher of the Alachua County Sheriff's Office said her office is "trying to do the best we can to track down the originator" of the messages but she said a deeper inves
