On Wednesday, the Supreme Court issued what is probably its single most consequential ruling of the year. Janus v. AFSCME is a devastating blow against public sector unions, barring them from charging “agency fees” to the public employees for whom they negotiate pay increases and benefit bumps if those employees decline to join the union as full members.

Now, teachers unions, police unions, and more will be forced to lobby public employees to pay full union dues, even though those employees will get the same benefits from the union if they pay nothing at all.

You can read our full explainer on the case here, but it’s worth diving into the actual language of Justice Samuel Alito’s 5-4 majority opinion and Justice Elena Kagan’s dissent in more detail to understand exactly why the Court decided to make the whole United States adopt a “right-to-work” policy when it comes to public employees.

1) The Court has overruled a decision it made in 1977

Janus is a rare Supreme Court decision (though the second in this term) that overrules a previous judgment of the Court. The Supremes generally abide by a principle known as stare decisis, Latin for “to stand by things decided.” That means that even if justices believe a past decision was wrongly decided, they generally accept it as precedent and rule in accordance with it going forward.

The previous decision Janus overrules is known as Abood v. Detroit Board of Education, decided back in 1977. Detroit teacher D. Louis Abood objected to being forced to become a member or pay agency fees (which are generally lower but pay for bargaining services) to a teachers union. To force him to give money to a group whose political ideas he disagreed with was, he claimed, compelled speech.

In a unanimous ruling, the Court rejected that argument, instead ruling that while agency fees could not be used to pay for lobbying or political activity, unions could still force nonmembers to pay them in exchange for collective bargaining and other apolitical services the union provides.

Many conservatives, and Alito in particular, have argued for years that Abood was incorrectly decided. Alito used majority opinions in 2012’s Knox v. SEIU and 2014’s Harris v. Quinn to detail the decision’s flaws, with an eye toward eventually overturning it in full (which the Court’s liberals warned in dissents in those cases was his eventual game plan). With Janus, he got a chance to go all the way, and cited his own decisions in Knox and Harris repeatedly:

We upheld a similar law in Abood v. Detroit Bd. of Ed., 431 U. S. 209 (1977), and we recognize the importance of following precedent unless there are strong reasons for not doing so. But there are very strong reasons in this case. Fundamental free speech rights are at stake. Abood was poorly reasoned. It has led to practical problems and abuse. It is inconsistent with other First Amendment cases and has been undermined by more recent decisions.Developments since Abood was handed down have shed new light on the issue of agency fees, and no reliance interests on the part of public-sector unions are sufficient to justify the perpetuation of the free speech violations that Abood has countenanced for the past 41 years. Abood is therefore overruled. … In Abood, the Court upheld the constitutionality of an agency-shop arrangement like the one now before us, but in more recent cases we have recognized that this holding is “something of an anomaly,” Knox v. Service Employees (2012), and that Abood’s “analysis is questionable on several grounds,” Harris. We have therefore refused to extend Abood to situations where it does not squarely control, see Harris, while leaving for another day the question whether Abood should be overruled, Harris, Knox. We now address that question.

2) The Court’s conservatives view making public employees pay agency fees as an unacceptable First Amendment violation

Alito’s beef with Abood has always been that merely separating out the political and apolitical parts of union fees is not sufficient to respect employees’ First Amendment rights. If non-union supportive employees are forced to pay agency fees to avoid a free-rider problem and ensure that unions have adequate funding to bargain for their members, then those employees are effectively being coerced into funding speech with which they disagree. Coerced speech has traditionally been considered a major First Amendment violation, and Alito argues that this case should not be treated as an exception:

Compelling individuals to mouth support for views they find objectionable violates that cardinal constitutional command, and in most contexts, any such effort would be universally condemned. Suppose, for example, that the State of Illinois required all residents to sign a document expressing support for a particular set of positions on controversial public issues—say, the platform of one of the major political parties. No one, we trust, would seriously argue that the First Amendment permits this. Perhaps because such compulsion so plainly violates the Constitution, most of our free speech cases have involved restrictions on what can be said, rather than laws compel­ling speech. But measures compelling speech are at least as threatening. … Compelling a person to subsidize the speech of other private speakers raises similar First Amendment con­cerns. As Jefferson famously put it, “to compel a man to furnish contributions of money for the propagation of opinions which he disbelieves and abhor[s] is sinful and tyrannical.” We have therefore recognized that a “ ‘significant impingement on First Amendment rights’” occurs when public employees are required to provide financial support for a union that “takes many positions during collective bargaining that have powerful political and civic consequences.”

3) Alito doubts that this decision will hurt public-sector unions as much as they fear

It does not suffice, especially when overturning a 41-year-old precedent, to merely argue that a law burdens free speech. The Court typically takes a strong presumption against any burdening of free speech, but when a compelling interest is at stake — like a need to prevent free-riding on the union’s bargaining ability, and the union’s need to be compensated for the work it does to raise worker wages — that interest can trump an apparent burdening of speech.

The question in these cases is always how to weigh that burden on speech and the interest being served in burdening it. As Justice Kagan would write in her Harris v. Quinn dissent in 2014, “Our decisions have long afforded government entities broad latitude to manage their workforces, even when that affects speech they could not regulate in other contexts.”

So Alito is forced to reckon with the arguments that defenders of agency fees make. He begins by attacking the argument in Abood that agency fees serve the government’s interests by encouraging “labor peace”:

By “labor peace,” the Abood Court meant avoidance of the conflict and disruption that it envisioned would occur if the employees in a unit were represented by more than one union. In such a situation, the Court predicted, “inter-union rivalries” would foster “dissension within the work force,” and the employer could face “conflicting demands from different unions.” Confusion would ensue if the employer entered into and attempted to “enforce two or more agreements specifying different terms and conditions of employment.” And a settlement with one union would be “subject to attack from [a] rival labor organizatio[n].”

Alito claims this is factually incorrect, and that banning agency fees wouldn’t cause this kind of chaos. His argument is that employees will still flock toward, and pay dues to, a sole union, preventing labor conflict of the kind the Abood Court feared:

The federal employment experience is illustrative. Under federal law, a union chosen by majority vote is designated as the exclusive representative of all the em­ployees, but federal law does not permit agency fees. Nevertheless, nearly a million federal employees—about 27% of the federal work force—are union members. The situation in the Postal Service is similar. Although permitted to choose an exclu­sive representative, Postal Service employees are not required to pay an agency fee, and about 400,000 are union members. Like­wise, millions of public employees in the 28 States that have laws generally prohibiting agency fees are represented by unions that serve as the exclusive representatives of all the employees. Whatever may have been the case 41 years ago when Abood was handed down, it is now unde­niable that “labor peace” can readily be achieved “through means significantly less restrictive of associational free­doms” than the assessment of agency fees.

This section serves an argumentative purpose in the context of the ruling. But it also serves a PR purpose, to explain that Alito does not believe he is gutting the public employee movement, but instead is denying it a privilege that is not necessary for its continued thriving.

The Court is reasonably sensitive, even in cases like this when it’s effectively engaging in policymaking, to claims that it’s overreaching and undemocratically making major political decisions. This is Alito’s way of pushing back on that claim, and insisting that public sector unions will be all right regardless.

4) Alito is deeply worried about the political economy effects of public unions

Alito, in his opinion, has to rebut the idea that union speech in the context of collective bargaining is essentially apolitical, and about wages and benefits for workers. If it’s speech made as a matter of course during normal business hours, then the claim that compelling that speech violates the First Amendment is dubious. Otherwise, if, say, you work at the DMV and your boss orders you to go talk to someone waiting for a driving test, that order could be construed as “compelled speech.” That’s obviously ridiculous, and a result the Court wants to avoid.

So Alito avoids it by arguing that everything that public sector unions do in collective bargaining is political, and has major political ramifications. In particular, he doesn’t appear to like what it’s done to pensions and public sector spending:

Illinois, like some other States and a number of counties and cities around the country, suffers from severe budget problems. As of 2013, Illinois had nearly $160 billion in unfunded pension and retiree healthcare liabilities. By 2017, that number had only grown, and the State was grappling with $15 billion in unpaid bills. We are told that a “quarter of the budget is now devoted to paying down” those liabilities. These problems and others led Moody’s and S&P to downgrade Illinois’ credit rating to“one step above junk”—the “lowest ranking on record for a U.S. state.” The Governor, on one side, and public-sector unions, on the other, disagree sharply about what to do about these problems. The State claims that its employment-related debt is “‘squeezing core programs in education, public safety, and human services, in addition to limiting [the State’s] ability to pay [its] bills.’” It therefore “told the Union that it would attempt to address th[e financial] crisis, at least in part, through collective bargaining.” And “the State’s desire for savings” in fact “dr[o]ve [its] bargaining” posi­tions on matters such as health-insurance benefits and holiday, overtime, and promotion policies. But when the State offered cost-saving proposals on these issues, the Union countered with very different sugges­tions. Among other things, it advocated wage and tax increases, cutting spending “to Wall Street financial insti­tutions,” and reforms to Illinois’ pension and tax systems(such as closing “corporate tax loopholes,” “[e]xpanding thebase of the state sales tax,” and “allowing an income tax that is adjusted in accordance with ability to pay”). To suggest that speech on such matters is not of great public concern—or that it is not directed at the“public square”—is to deny reality.

He further cites the example of teacher union influence on education policy. Collective bargaining negotiations in education often touch on highly contentious policy issues around tenure and merit pay that are clearly political in nature:

Speech in this area also touches on fundamental ques­tions of education policy. Should teacher pay be based on seniority, the better to retain experienced teachers? Or should schools adopt merit-pay systems to encourage teachers to get the best results out of their students? Should districts transfer more experienced teachers to the lower performing schools that may have the greatest need for their skills, or should those teachers be allowed to stay where they have put down roots? Should teachers be given tenure protection and, if so, under what conditions? On what grounds and pursuant to what procedures should teachers be subject to discipline or dismissal? How should teacher performance and student progress be measured—by standardized tests or other means?

He returns to these themes later in the opinion, to argue that the landscape of public sector unions has changed since Abood, largely (in his view) because the unions have gotten more powerful and are responsible for a large increase in government spending:

This ascendance of public-sector unions has been marked by a parallel increase in public spending. In 1970, total state and local government expenditures amounted to $646 per capita in nominal terms, or about $4,000 per capita in 2014 dollars. By 2014, that figure had ballooned to approximately $10,238 per capita. Not all that increase can be attributed to public-sector unions, of course, but the mounting costs of public-employee wages, benefits, and pensions undoubtedly played a substantial role. We are told, for example, that Illinois’ pension funds are underfunded by $129 billion as a result of generous public-employee retirement packages. Unsustainable collective-bargaining agreements have also been blamed for multiple municipal bankruptcies. These developments, and the political debate over public spending and debt they have spurred, have given collective-bargaining issues a political valence that Abood did not fully appreciate.

5) Public employee union membership has to be opt-in now, not opt-out

Alito’s opinion was even more anti-union than many observers expected. Not only did it end agency fees for public employees, but it required, for the first time, that union membership for new public employees be “opt-in” rather than opt-out:

Under Illinois law, if a public-sector collective-bargaining agreement includes an agency-fee provision and the union certifies to the employer the amount of the fee, that amount is automatically deducted from the non­member’s wages. No form of employee consent is required. This procedure violates the First Amendment and can­not continue. Neither an agency fee nor any other pay­ment to the union may be deducted from a nonmember’s wages, nor may any other attempt be made to collect such a payment, unless the employee affirmatively consents to pay. By agreeing to pay, nonmembers are waiving their First Amendment rights, and such a waiver cannot be presumed.

There is considerable economic and psychological evidence supporting the idea that automatic or opt-out programs dramatically increase take-up. One study using Danish data found that about 85 percent of people, when automatically switched to contributing more to their pensions, will continue to do so, whereas only a small share of people reduce savings when subsidies for savings are cut because in the latter case they have to affirmatively change their behavior rather than just going with the flow.

That suggests that switching union enrollment from opt-out to opt-in could substantially reduce union membership going forward. That’s another blow that unions weren’t really expecting from this ruling.

6) Kagan argues this ruling throws stare decisis out the window

In her dissent, Kagan issues a passionate defense of Abood against Alito’s criticisms, answering him point by point. But her more fundamental concern is that Alito and the Court’s conservatives are effectively abandoning stare decisis and saying that they can throw out precedents they dislike whenever they want to do so:

Abood is not just any precedent: It is embedded in the law (not to mention, as I’ll later address, in the world) in a way not many decisions are. Over four decades, this Court has cited Abood favorably many times, and has affirmed and applied its central distinction between the costs of collective bargaining (which the government can charge to all employees) and those of political activities (which it cannot). Reviewing those decisions not a decade ago, this Court—unanimously—called the Abood rule “a general First Amendment principle.” … And in any event, one stare decisis factor—reliance— dominates all others here and demands keeping Abood. Stare decisis, this Court has held, “has added force when the legislature, in the public sphere, and citizens, in the private realm, have acted in reliance on a previous decision.” That is because overruling a decision would then “require an extensive legislative response” or “dislodge settled rights and expectation.” Both will happen here: The Court today wreaks havoc on entrenched legislative and contractual arrangements. Over 20 States have by now enacted statutes authorizing fair-share provisions. To be precise, 22 States, the District of Columbia, and Puerto Rico—plus another twoStates for police and firefighter unions. Many of those States have multiple statutory provisions, with variations for different categories of public employees. Every one of them will now need to come up with new ways—elaborated in new statutes—to structure relations be-tween government employers and their workers. The majority responds, in a footnote no less, that this is of no proper concern to the Court.

Her conclusion is blistering and pulls no punches: