The 7th Circuit Court of Appeals rejected Janus’ argument, and the Supreme Court agreed to hear his appeal.

If the Supreme Court finds for Janus, it could have a major effect on labor unions. Without compulsory fees, union funding could decrease precipitously. States might attempt workarounds — paying employees less rather than deducting from their paychecks, and passing along the savings to unions — but that sort of thing could be politically difficult to pull off.

“The merits of the case, and 40 years of Supreme Court precedent and sound law, are on our side,” says Lee Saunders, president of AFSCME.

For Saunders, strong unions are important because they offer “the strength in numbers [workers] need to fight for the freedoms they deserve,” such as health care and retirement plans.

“The merits of the case, and 40 years of Supreme Court precedent and sound law, are on our side.”

- Lee Saunders, president of AFSCME

The central question in “Janus” is this: Should the court overrule its 1977 decision “Abood v. Detroit Board of Education”? In “Abood,” the Supreme Court declared that schoolteachers could be required to pay fees to public unions as long as the money was spent on the costs of collective bargaining and related issues, and not on ideological causes.

Court watchers may be getting a sense of déjà vu from “Janus” -- in the past several years, the Supreme Court has already looked at this question a couple of times.

And they might have done just that, except that Associate Justice Scalia died before the case could be decided. This left the court split with four liberals and four conservatives, so they simply put out a one-line opinion that affirmed the lower court decision, leaving the question for another day.

And now, with “Janus,” that day has come.

The biggest change since “Friedrichs” then, is not the facts of the case, but the makeup of the court. Scalia has been replaced with Associate Justice Neil Gorsuch, and many believe he’ll be the fifth vote to overturn “Abood.” (If President Barack Obama’s choice to replace Scalia, Merrick Garland, had been seated, it’s possible the court wouldn’t even be hearing the “Janus” case.)

In fact, many experts see the decision to take up the case as a sign that the court is ready to side with Janus and overrule their precedent.

As Fox News legal analyst Judge Andrew Napolitano notes, “Justice Gorsuch . . . is pretty much a champion of the choice of individuals in this type of environment.” Add that to the four justices already leaning his way, and it looks like they’re ready to hand Janus a victory.

Many states might not be happy with such a ruling, but, as Napolitano notes, the First Amendment supersedes state arrangements with labor. Indeed, Napolitano, a civil libertarian, would hail a decision on behalf of Janus, and hopes “everyone who believes that the First Amendment means what it says would applaud.”

One argument against changing “Abood” is that it is firmly established law and the states have learned how to work with it — now is not the time to overturn it.

A change in the law, many fear, could turn quite a few workers into free riders who won’t have to pay for the unions but will still get to enjoy the benefits of collective bargaining.

Volokh doesn’t see why union fees should be treated any differently.

For his part, Napolitano can’t summon up too much sympathy for these unions, since they’ve gotten themselves into this situation. As he puts it, “some labor leaders believe this will be almost a fatal blow — you know what, that’s their fault….No one is saying that labor unions [shouldn’t] exist; they just have to make themselves attractive so that people join voluntarily, rather than under the state’s compulsion.”

Fox News’ Kristine Kotta contributed to this report