Dubbed “Sharpiegate” by conservatives on social media, the allegations could be used to try to undermine election results in the historically Republican state of Arizona, which the Associated Press called for Democratic presidential candidate Joe Biden with 51% of the vote.
Similar rumors about Sharpies or other writing tools and ballots have circulated in Chicago, Michigan, Massachusetts and Connecticut in recent days.
Maricopa County officials were trying to inform voters that Sharpies did not interfere with ballots.
The county - which includes Arizona's biggest city, Phoenix - last year rolled out new tabulation equipment that made Sharpie pens the best option on Election Day because they have the fastest drying ink, said Megan Gilbertson, the Maricopa County Elections Department's communications director.
The department posted a video on Election Day clarifying that Sharpies would not interfere with ballots.
“The Sharpies are just fine to use," Gilbertson said in an interview. "They do not impact tabulation, and we encourage them on Election Day because of how fast the ink dries."
By Tuesday night, some Arizona Trump voters had begun to question whether ballots had been counted.
Andrea Thiele, 48, of Surprise, Arizona, said in an interview that when she took her daughter to vote, she’d noticed Sharpies and found them “fishy.”
The voting machine accepted her daughter’s ballot, she said.
Later, however, she discovered a viral Facebook video saying that Trump voters had their ballots rejected after Maricopa County poll workers had given voters Sharpies.
Now, she is concerned the ballot wasn’t counted.
“I suspect there’s fraud happening, absolutely,” she said.
The state attorney general’s office said in a statement to Reuters on Wednesday it had received hundreds of complaints about Sharpie use and said it had sent a letter to Maricopa County officials to investigate the concerns.
By Wednesday afternoon, the video Thiele saw had been shared on Facebook 101,000 times, and had been promoted by prominent conservatives, including Sidney Powell, the attorney representing former Trump national security adviser Michael Flynn.
Following those 101,000 shares, it was labeled "false information" on Facebook by fact-checkers who have partnered with the social media company to root out disinformation about the 2020 election.
Facebook has also blocked the hashtag "#sharpiegate," Facebook spokeswoman Andrea Vallone said, while a Twitter spokeswoman said the social media company is labeling tweets that "misleadingly claim ballots were invalidated."
American Conservative Union Chairman Matt Schlapp has also repeated the fraud claims on Twitter and urged voters to report them to the Arizona attorney general’s office.
Schlapp and Powell could not immediately be reached for comment.
Alex Stamos, Facebook's former chief technology officer and now director of the Stanford Internet Observatory, told reporters Wednesday the allegations were “disinformation.”
“Once this idea was out there in the zeitgeist, it was picked up,” he said. “After Fox News called Arizona for Vice President Biden, all of a sudden you see the exact same narrative repurposed specifically about Arizona without any kind of evidence."