Garden suspects that since Alito wrote the opinions in Knox and in Harris, he’s the one driving these cases. And he seems ready to dismantle Abood, writing that it causes administrative headaches as unions distinguish between political and non-political causes.

Unlike the two cases that preceded it, Friedrichs takes on the question of fees—one that is essential to all public-sector unions—in the field that is perhaps the most essential to public-sector unions: education. The Friedrichs argument posits that even bargaining intended to directly benefit teachers is political. Governments are low on money, it argues, and people represented by unions might not agree with union leadership that they should receive raises from a cash-strapped system, for example, or that more money should be spent on education.

“It is difficult to imagine more politically charged issues than how much money local governments should devote to public employees, or what policies public schools should adopt to best educate children,” the brief argues.

A decision against unions in Friedrichs could severely weaken unions’ bargaining and financial power. Under federal law, if a majority of employees decide to form a union, the union must represent all employees for bargaining purposes. But if some people decide not to join (whether because of genuine political disagreement or merely to save money on the fees), the union has less leverage because it represents fewer members. It also has less money to pay for the things that keep it strong, like bargaining and organizing. But it still has an obligation to do things such as bargaining and organizing since, in many states, public employers are required to bargain with unions.

“Reading the tea leaves, I think there is cause for public-sector unions to be concerned,” Garden said.

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A ruling against unions would not kill the labor movement for good, experts say. But it would severely harm it. Though the case’s concerns are limited to public-sector unions, the public sector is one of the only reliably organized sectors left in the country. About 35 percent of public-sector workers, or 7.2 million workers, belonged to a union in 2014, the most recent year for which there is data available, according to the Bureau of Labor Statistics. In that same year, only 6.6 percent of the private sector, or 7.4 million workers, was unionized. The percentage of public-sector workers who are unionized has remained relatively constant over recent years, while the percentage for the private sector has continued to shrink.

If the Court decides in Friedrichs’s favor, the ruling could essentially make being in a public-sector union anywhere akin to joining a private-sector union in a right-to-work state. In the nation’s 25 right-to-work states, private-sector members do not have to join unions as a condition of employment—even at unionized shops—nor do they have to pay dues. And when workers don’t have to pay dues, they often choose not to, because they can get the benefits of a union’s collective bargaining for free because they are still represented by the unions. (A UC Irvine professor has recently argued for allowing unions to only represent people who pay dues, but that would require changes to the National Labor Relations Act.)