Outside the door to Linda Hagen's third-grade classroom at Turtle Lake Elementary in Shoreview, there's a sign that reads: "I will vote."

She sees the same sign posted by many other teachers outside their classrooms. Each has a photo of a teacher's face, the promise to cast a ballot, and the name of the organization leading the charge to the polls: Education Minnesota, the state teachers union.

Long an influential force in state politics, raising and spending millions on campaigns and funding lobbyists at the State Capitol, Education Minnesota is taking a new tack as it faces a high-stakes election. As usual, the union is looking to sway voters with its high-profile endorsements and big campaign rallies. But this year, it's also aiming at a particular subset of would-be voters: its own members.

"There's more of a buzz than I've ever heard before around election time," Hagen said.

For the union, there are plenty of reasons this election matters. A recent U.S. Supreme Court ruling forbids unions from requiring nonmembers to help cover the cost of collective bargaining — threatening the union's financial position and prompting a flurry of activity from outside groups who say they've heard from many teachers who are unhappy with Education Minnesota.

Meanwhile, wide-open races for governor, attorney general and other seats have union leaders concerned that Minnesota could follow states like Wisconsin and Iowa in weakening the position of public-sector unions or making dramatic shifts in education policy.

If Education Minnesota wants to avoid that fate, it needs to lean on the full power of its 90,000 members, said Denise Specht, the union's president.

"If we are not making sure that our voices are heard in this election, you never know what's going to happen after," she said.

The union began re-evaluating its political strategy after the 2016 election. For a group that almost exclusively supports DFL candidates and policies, things had not gone well: Republicans held on to their majority in Congress and won the White House, and the Minnesota Senate flipped from DFL to Republican control, ensuring an uphill battle for many of Education Minnesota's priorities.

Union officials lined up their roster alongside state voting records and found something startling: More than a third of their members — some 33,000 voters — had sat out the last midterm election.

"That's enough to swing a statewide race," Specht said. "That's a lot of people."

Meanwhile, the union was anticipating the Supreme Court's ruling and subsequently, a possible drop in membership. To maintain its numbers, Education Minnesota would need to fortify its membership and bank accounts. Last year, the union increased the amount deducted from each member's annual union dues for its political action committee from $15 to $25. (If members want to opt out of that donation, they have to jump through a few hoops: Fill out a form included in an issue of the union's magazine — and not a photocopied version — and submit it by the end of October, or within 30 days of signing on as a union member.)

Leaders also realized they'd need to do more to refine their membership sales pitch, especially to the approximately 5,000 nonmembers who no longer had to contribute to the union's collective bargaining efforts. At the same time, conservative groups like the Center of the American Experiment began appealing to those teachers and full-fledged members to leave the union — and reported some success.

By the time the school year rolled around, the union had refined its strategy. Sorting through the voting lists, leaders picked out the schools where at least 10 of its members hadn't voted in 2016. In each of those buildings, they enlisted another teacher to serve as a "worksite action leader." Across the state, those leaders have organized after-school socials at breweries and restaurants where they make a pitch for voting, held raffles and political-themed trivia nights and urged their co-workers to make a plan for voting before or on Election Day.

Some of the building leaders are themselves new to politics. Cassidy Baker, an early childhood special education teacher in the Mounds View district, said political activity has typically been outside of her comfort zone. But this year, she said, "I felt like my livelihood and the level of quality education I'm able to provide my students is on the line."

Erin Hester, a high school social studies teacher and peer coach in the Prior Lake-Savage district, said her efforts as a building leader have focused on the importance of being involved in the political process more than on specific candidates — and she's had only positive feedback.

"I think when we tell people: 'Hey, in the last major election, thousands of teachers didn't vote,' I think it's pretty shocking," she said.

Though the union has members who belong to both political parties, Education Minnesota has historically been one of the DFL's most powerful allies. This year, its slate of candidates for major state offices is exclusively DFL, and its sizable campaign contributions have gone almost entirely to candidates and committees on the political left. (Through September, the union's political action committee gave roughly $1.2 million to DFL campaigns and committees, $62,653 to local Education Minnesota political organizations and $300 to the House Republican Campaign Committee.)

The higher political fees for members have helped the union raise more campaign cash this year than in previous midterm election cycles; by September, the Education Minnesota PAC had raised more than $2.7 million. That's more than double what it raised in the entire year in both 2010 and 2014.

Education Minnesota has not released updated membership numbers this fall, so it's still unclear if the union is heading into the election and next year's legislative session with a smaller or larger roster. Charlie Weaver, executive director of the Minnesota Business Partnership, an organization of major companies that's a similarly powerful force on the other side of the political aisle, said he doesn't expect there will be much of a blip in Education Minnesota's agenda. He said any drop in the union's membership or power would take time to have a major impact.

"They are a worthy adversary, from my perspective," he said. "I'm sure we'll be bumping heads this session."