“This was a mistake,” said Madison city spokesperson Dylan Brogan. “On the day we found out a clerical error occurred, we immediately reached out to voters.”

The ballot error in the Democratic stronghold, which happens to be in a battleground state, is prompting calls from Republicans, including Wisconsin Rep. Tom Tiffany, to investigate.

“The city of Madison clerk said the duplicate absentee ballots were sent to one ward yesterday. Now, they say it’s 10. There needs to be an independent investigation now, not after the election,” Tiffany wrote Wednesday in a post on X.

“Although the Madison Clerk’s Office claims ‘The voting system does not allow a ballot with the same barcode to be submitted,’ my office has proof that there is no barcode on the actual ballots,” Tiffany added in a separate post on X, along with a photo of an absentee ballot.

Madison city officials said: “The error affected only an isolated number of voters and was quickly caught and corrected so that it will not affect any other ballots going forward.”

The clerk’s office confirmed it has been contacting the voters individually and has cautioned them to submit only one ballot and to destroy the second one “to avoid any confusion.”

“The voter is also marked in the poll book as having submitted their absentee ballot as another safeguard against the voter submitting a second ballot,” the city said.

Tiffany sent a letter Tuesday to Madison city officials, asking them to provide information on how the error was discovered and why it occurred.

“Voters deserve clear answers regarding the full scope of this blunder, how the city plans to restore public confidence in its ability to accurately administer the election and assurances that those responsible are held accountable,” the letter said.