When Allan Bruner set up a booth for the Oregon Education Association at the annual gathering of the Republican Party of Oregon earlier this year, he was operating behind what many teachers consider enemy lines.

"We got a lot of looks," says Bruner, a 25-year classroom veteran who teaches in the Colton School District in Clackamas County. "People said, 'What are you doing here?'"

In Oregon, teachers and Republicans don't usually mix. Perhaps no group has contributed more to Democratic dominance of state politics than the 45,000-member teachers union. OEA has given $4 million directly since 2006 and leveraged more from affiliates.

Bruner is a rarity—an OEA member who is also a registered Republican.

Union critics are trying to end what they see as the Democratic Party's coercion of non-Democratic union members.

That battle, both in Oregon and nationally, has profound implications for a 2016 ballot fight that could lead to the largest tax increases in more than a decade.

Labor unions are the biggest backers of up to $5 billion in tax measures planned for the 2016 ballot. But some union members aren't political supporters of new taxes.

Jill Gibson is a Portland lawyer representing Republican interests seeking to weaken union support for Democrats through so-called "right-to-work" ballot measures.

Earlier this month, Gibson and former Lewis & Clark College law dean James Huffman filed a brief in a related U.S. Supreme Court case containing numbers that reveal a surprising fact: Unions are not nearly as Democratic as their giving suggests.

"Fifty-two percent of Oregon teachers are registered Democrats, 25 percent are registered Republicans, and 24 percent are unaffiliated or belong to minor political

parties," Gibson and Huffman wrote in the brief filed Sept. 11.

"Since 2006," the brief continues, "Oregon teacher unions have contributed over $4 million to political candidates, and approximately 98 percent of that amount has gone to Democratic candidates."

In their brief, Gibson and Huffman argue that public employees who are not Democrats are forced to contribute to causes in which they may not believe. If they could change that, the argument goes, they might change election outcomes.

BethAnne Darby, an OEA lobbyist, says the lawyers' figures are slightly misleading. Darby says the $4 million is an accurate figure, but it represents teachers' voluntary contributions to a political action committee over and above their union dues.

Only about 11 percent of teachers who contribute to the OEA political action committee are registered Republicans, although a Republican chairs the PAC. Darby says the union makes its endorsements and contributions in a democratic ("with a small d") process that is fair to all members.

There's no disputing, however, that combined with contributions from Service Employees International Union and the American Federation of State, County and Municipal Employees, OEA's money has helped Oregon Democrats win legislative majorities and every statewide office.

Republicans have launched a two-pronged attack on that dominance. Earlier this year, Gibson filed two right-to-work

ballot measures aimed at making it easier for public employees to opt out of supporting Democratic candidates and causes.

Gibson received unfavorably worded ballot titles for those measures, however, and is now drafting new versions.

A similar issue is in front of the U.S. Supreme Court in a case called Friedrichs v. California Teachers Association. Observers, including leaders of the Oregon unions Gibson targeted, expect the court to rule in the middle of next year on the Friedrichs case—and they expect the court to rule against union interests.

"We think the Supreme Court case would do substantially the same thing as the Oregon ballot measures were supposed to do," says AFSCME's state political director, Joe Baessler. "It would weaken the unions."

Gibson and Huffman illustrated the issue in the friend-of-the-court brief they filed in the case. Their clients, state employees Glenn Schworak and James Mitchell, belong to SEIU, Oregon's largest labor union, but disagree with the union's politics.

Every year, SEIU deducts $1,488 each from the men's paychecks. They have opted out of SEIU's political program, so each gets $300 back. They contend the process for opting out is onerous, however, discouraging other members from following suit.

The looming court decision has implications for what is shaping up as the biggest battle on the 2016 ballot: the effort by Our Oregon, an advocacy group funded by public employees, to raise between $1 billion and $5 billion in new taxes. That would be a far larger increase than tax increases that split the state in 2007.

Two years ago, then-Gov. John Kitzhaber brokered a truce between business and labor that avoided a ballot battle over new taxes.

The threat of reduced union membership and financial muscle makes it unlikely any such diplomacy will derail new tax measures in 2016.

Union leaders say chances of passing new taxes are greater in a presidential election year, which in Oregon spells a large Democratic turnout, and it doesn't hurt that the state's business lobby is in disarray ("The Unger Games," WW, Sept. 2, 2015).

"There are a lot of people who think we need to go to the ballot now," Baessler says, "and if the Supreme Court decides against us, we're going to have to be more aggressive."