The most consequential decision to come out of the United States Supreme Court’s current term isn’t, despite the headlines, Masterpiece Cakeshop, dubbed in popular media as “the gay wedding cake” case. Nor is it NIFLA v. Becerra, the lesser-known case about what disclosures the state of California could require of unlicensed faith-based “pregnancy crisis” centers. Instead, the case with the most significant implications—for workers, for the LGBT community, and for women—is almost certainly Janus v. AFSCME, decided by the Court last Wednesday.

On the surface, that may seem surprising given the nature of the question presented in Janus. Mark Janus is an employee with the Illinois Department of Healthcare and Family Services, where employees are represented by Council 31 of the American Federation Of State, County, and Municipal Employees (AFSCME). Janus wasn’t a union member, but he was protected by a collective bargaining agreement AFSCME negotiated. But because Janus wasn’t a union member, he didn’t want to pay money to the union.

Illinois, like nearly half of all states, allows public unions to charge certain fees to those non-members for the service they provide. Those fees, called “agency fees” or “carrier fees,” are less than standard union dues, and have been generally permissible since Abood v. Detroit Board of Education in 1977. Writing for a unanimous Court, Justice Potter Stewart wrote that

The designation of a union as exclusive representative carries with it great responsibilities. The tasks of negotiating and administering a collective-bargaining agreement and representing the interests of employees . . . often entail expenditure of much time and money. . . . A unionshop arrangement has been thought to distribute fairly the cost of these activities among those who benefit, and it counteracts the incentive that employees might otherwise have to become "free riders" to refuse to contribute to the union while obtaining benefits of union representation that necessarily accrue to all employees.

It’s worth noting that Abood wasn’t really that controversial at the time–it was decided unanimously, in fact. And the Abood court took great care to hold that a state “cannot constitutionally compel public employees to contribute to union political activities which they oppose[,]” thereby differentiating between monies paid to unions for the purposes of collective bargaining and monies paid to unions for political purposes. That’s one of the reasons that agency fees are less than union dues–they don’t fund the union’s political activities.

But since Abood, conservative legal thought has generally evolved towards the theory that it was wrongly decided. That’s for a couple of reasons – one legal, and one practical. The practical reason was simply that unions, particularly public unions, tend to support overwhelmingly Democratic candidates and causes. And from a legal perspective, the theory went that a public union requiring the payment of agency fees by non-members violates the First Amendment rights of those non-members. The First Amendment guarantees the right of persons not just to freedom of speech and religion, but also something called “freedom of association.” Freedom of association is essentially your right to join, or not to join, a group of people; it’s what prohibits a state from passing a law requiring people to join a political party, for example.

And so Governor Rauner sued AFSCME, saying that the fees paid by non-members to unions violated the First Amendment. Janus joined the suit as a plaintiff, and the suit eventually reached the Supreme Court, where Abood was swiftly and unceremoniously overruled.

In fact, Justice Alito, writing for the conservative majority, was merciless in his characterization of Abood, calling it a “poorly reasoned” decision which “has led to practical problems and abuse” and is “inconsistent” with the First Amendment. “[N]o reliance interests on the part of public-sector unions,” wrote Alito, “are sufficient to justify the perpetuation of the free speech violations” which Abood caused. But Alito also wrote an opinion with eyes fixed squarely on the crippling blow to public sector unions he was drafting. “We recognize,” he wrote, “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.”

But it’s not just the damage to public unions which makes Janus the most significant development to come out of this Court term. Unlike the narrow decision in Masterpiece Bakeshop, the decision in Janus was no compromise; it was conservative thought, fully realized in the form of judicial opinion. And unlike NIFLA, where the Court took pains to avoid at least the appearance of upending precedent, in Janus the conservative wing had no such compunctions, overruling Abood in its entirety. As Justice Kagan wrote in dissent, “Rarely if ever has the Court overruled a decision—let alone one of this import—with so little regard for the usual principles of stare decisis.  . . . [I]t is deeply entrenched, in both the law and the real world. More than 20 States have statutory schemes built on the decision. Those laws underpin thousands of ongoing contracts involving millions of employees.”

Kagan’s dissent sounds a warning for court watchers. Abood was as deeply entrenched as Roe v. Wade, and far more so than the 2015 decision in Obergefell v. Hodges, which guaranteed the right of same-sex couples to marry–and now it’s gone. And Anthony Kennedy, the swing vote protecting Roe and Obergefell, is retiring on July 31, likely to be replaced by a far more conservative successor. Janus was a canary in the coal mine; its opinion heralds the realization that Roe and Obergefell are very much in danger.