Anti-union forces in the Republican Party today realized their long-held hope of undercutting some of the power of public employee unions when the U.S. Supreme Court voted 5-4 to overturn the long-held principle that union members who benefit from collective bargaining should help pay for the costs.

The effect of the court's ruling in a case from Illinois—Janus vs. the American Federation of State, Country and Municipal Employees union—will be to weaken the financial muscle and the membership numbers of one of the bulwarks of the Democratic Party.

There are few states where public employee unions enjoy the clout they do in Oregon, for two reasons: first, Oregon is an predominantly Democratic state in terms of voter registration, with Democrats outnumbering Republicans by 260,000 or about 10 percent of the electorate; and more importantly, Oregon is one of only half a dozen states with no restrictions on campaign contributions, which means unions can spend as much as they want in candidate and ballot measure races.

That has helped Oregon's three largest public employee unions, Service Employees International, the Oregon Education Association and AFSCME become powerhouses and helped Our Oregon, the political non-profit that gets much of its funding from those three groups, dominate ballot measures for more than a decade.

Responding to today's decision, SEIU president Melissa Unger said in a statement that Oregon's unions will take the ruling in stride.

"In 2014, the Supreme Court handed down a Janus-type decision against homecare workers," Unger said. "Four years later, SEIU 503's homecare workers are stronger and more united than ever—and through their unity and strength, they won one of the highest homecare wages in the nation."

The U.S. Supreme Court, which because of President Donald Trump's appointment of Justice Neil Gorsuch, is dominated by a conservative majority, dispensed with the so-called "free-rider" concept—i.e. the premise that because all members of a union benefit from collective bargaining they should all pay for it, and anybody who doesn't gets a "free ride."

"We recognize that the loss of payments from nonmembers may cause unions to experience unpleasant transition costs in the short term, and may require unions to make adjustments in order to attract and retain members," Justice Samuel Alito wrote, explaining the ruling. "But we must weigh these disadvantages against the considerable windfall that unions have received."

The court's more liberal justices disagreed.

"There is no sugarcoating today's opinion," wrote dissenting Justice Elena Kagan, according to the New York Times. "The majority overthrows a decision entrenched in this nation's law — and in its economic life — for over 40 years."

"As a result," she wrote, "it prevents the American people, acting through their state and local officials, from making important choices about workplace governance. And it does so by weaponizing the First Amendment, in a way that unleashes judges, now and in the future, to intervene in economic and regulatory policy."

The decision comes during a week of conservative rulings from the court, which has turned to the right after Trump appointed Gorsuch to the bench. Trump will likely appoint a second conservative justice to the bench because Justice Anthony Kennedy, a moderate conservative who voted with the more liberal members of the bench on cases involving gay rights, abortion, affirmative action and the death penalty, announced he will soon retire.