Madison teachers have voted overwhelmingly to retain their union.

Of the 2,838 Madison School District teachers eligible to vote, 86 percent cast a ballot to recertify the Madison Teachers Inc. union, according to the Wisconsin Employment Relations Commission, the state agency responsible for administering collective bargaining laws. The 20-day voting period ended at noon Tuesday.

Eligible voters who do not vote are counted the same as those who vote no. Of the 2,484 teachers who cast a ballot, 2,447 voted for the union and 37 voted against, for a 99 percent support rate.

“It speaks loud and clear that they value the union and what it’s done for them over the years and what it continues to do,” said John Matthews, an MTI executive.

The union also represents district employees in four other bargaining units: educational assistants, substitute teachers, support staff and security assistants. Members of all four of those bargaining units also voted in strong numbers to recertify.

For each of its five bargaining units, the union needed 51 percent of members to remain certified — an annual requirement set forth in Gov. Scott Walker’s signature 2011 legislation known as Act 10. The law significantly reduced collective bargaining rights for most public employees in Wisconsin.

Certification under Act 10 allows unions to continue to bargain over base wages. However, a teachers union can continue to exist and collect voluntary dues even if it isn’t certified. In those cases, administrators and school board members can choose to meet with union officials but are not obligated to do so.

“It’s a decision for each local union,” said Christina Brey at the Wisconsin Education Association Council, a statewide union for public school employees. “The advocacy doesn’t stop with or without certification.”

Certification costs money because the state levies a fee to cover the elections. Some unions decide the money and time are better devoted to efforts other than certification, Brey said.

MTI paid the state about $3,500 this year to oversee its elections.

Matthews said certification “helps us maintain our voice” and adds clout to the union’s discussions with administrators and School Board members.

Madison district officials and union representatives recently agreed on an employee handbook that will guide interactions when the current union contract expires next summer, having been made obsolete by Act 10. Both sides have pointed to the handbook as a positive collaboration that shows the continued value of employee input.

Because not voting counts the same as a no vote, unions work hard on their get-out-the-vote campaigns. To that end, MTI has argued it should have access to the names of teachers who have voted while the 20-day voting period is still going on.

That way, it could focus its outreach efforts on those who have not yet voted, Matthews said. The union is not seeking to know how a teacher voted, only whether he or she has already cast a ballot, he said.

Peter Davis, a WERC spokesman, said state commissioners have concluded that even providing a list of those who have voted would reveal too much, since usually almost everyone who votes in an election supports the union.

“Essentially, if you choose not to vote, you are exposing yourself as potentially someone who doesn’t support the union,” he said.

WERC does release the names of voters after the voting period ends because people need to have confidence in the accuracy of election results, Davis said. Matthews said the information does little good at that point.