A clerical mistake in the Madison city clerk's office means about 20 voters within the Madison School District got absentee ballots that do not have the district's $13 million referendum question on it, city and district officials said Tuesday.

Madison City Clerk Maribeth Witzel-Behl said six of those voters have come forward, and she urged other district residents who aren't sure if they voted on the question to call her office so her staff can destroy their old ballots and issue new ones.

Witzel-Behl said the mistake occurred because one of her employees created mailing labels for the absentee ballots' envelopes that did not identify the voter as a resident of the School District.

"My best guess is we're looking at less than 20 ballots total," she said.

Schools Superintendent Dan Nerad said the district learned of the problem late Monday in a phone call from the office of Madison Mayor Dave Cieslewicz.

Voters who alerted the city clerk's office that their absentee ballots did not include the referendum question "really became a signal that there was a problem here," he said.

Carole McGuire was one of those voters.

McGuire and her adult son — who is living with her and is registered to vote at her Southeast Side home — got different ballots, one that included the referendum question and one that did not.

"My concern as a former public official is if this happened to me, then who else has it happened to?" said McGuire, who has served on the Dane County Board and Madison City Council.

Witzel-Behl said that by Monday, her office had generated 14,310 absentee ballots, nearly 10,000 of which had been mailed to voters. She estimated that about 90 percent of those mailed were to addresses within the Madison School District. Seven other school districts also serve small parts of Madison.

"No matter what the number is (of faulty ballots), it's just really not acceptable," said Madison School Board President Arlene Silveira.