A suburban Twin Cities teachers union ran afoul of Minnesota's campaign finance disclosure rules after failing to file timely reports of its spending in the run-up to the November school board election, a panel of administrative law judges found.

That's because Dakota County United Educators reported spending nearly $29,000 for postcards, flyers and lawn signs when it was billed for them instead of when it placed the order, according to a campaign violation report issued by the state Office of Administrative Hearings.

Union President Kate Schmidt did not respond to a request for comment.

The union, which represents teachers and school nurses who work in the Rosemount-Apple Valley-Eagan district, submitted a list of expenditures in late October that left out the thousands of dollars the union agreed to pay for the campaign literature. The district is Minnesota's third largest.

Campaign finance records show the union reported $1,800 in expenses in its Oct. 26 report — $450 donations to each campaign of the four school board candidates it endorsed. But that report didn't include more than $36,000 in other expenses, including the printed material.

State law requires people and organizations to report disbursements within 10 days if they surpass $750 in expenses. The judges interpreted that to mean the disclosure law is triggered when a person or organization promises to pay for a service, not when they're billed for it.

"This promise falls within the definition of a disbursement and is, therefore, subject to reporting," the judges wrote.

Union officials filed two amended reports over the next week that detailed tens of thousands in costs for everything from lawn signs to postcards and newspaper ads. Education Minnesota, the statewide teachers union, had advised its Dakota County chapter to report those expenses when it was invoiced for them, according to the campaign violation report.

"That guidance conformed to past practice and our understanding of the law," Education Minnesota Executive Director Carrie Lucking said in a statement.

That guidance, according to judges Kimberly Middendorf, Jessica Palmer-Denig and Joseph Meyer, runs counter to the state's campaign finance disclosure laws. Union officials say they'll adjust their reporting recommendations.

"As a result, the guidance from Education Minnesota will be for local unions to report their expected expenses for campaign postcards before they receive an invoice for those expenses," Lucking said. "We anticipate this may affect the accuracy of initial disclosures of printing and mailing costs."

The judges determined the case was a technical and inadvertent violation of the state law because it came down to union officials' misinterpretation of the term "disbursement." The union was fined $100, among the least serious and costly of consequences the judges dole out because they concluded that it was easily countered and did not impact voters.