The theory of the “agency fee” is that non-members who benefit from the negotiations are “free riders.” So states may—if their legislatures wish—create an “agency fee” system in which the objectors pay only for the actual job-related bargaining costs. Union political activity, for example, is “non-chargeable,” because the First Amendment protects employees against subsidizing political speech to which they object. So the unions may collect from paychecks a fee only for the actual service they deliver.
In a 1977 case called Abood v. Detroit Board of Education, the Court gave its approval to the “free rider” argument. Objecting teachers in Abood had argued that all public-employee union activity was “political” in nature; thus, even subsidizing bargaining violated the First Amendment. The Court majority rejected that argument: “The differences between public- and private-sector collective bargaining simply do not translate into differences in First Amendment rights,” it said.
The Abood principle was reaffirmed, or at least applied, six times in the next two decades, most recently in 2009. Under ordinary circumstances, the Court is expected to stick with a precedent like this unless there’s something unusual about it—for example, that it has become unworkable, or conflicts with other rulings. The fact that some judges didn’t agree with it when it was first decided, without more, is not supposed to be enough. Thus, for example, Justice Sandra Day O’Connor, Anthony Kennedy, and David Souter almost surely disapproved of Roe v. Wade—but faced with a chance to overrule it, they refused, instead “reaffirming” a limited version. But Alito at some point after that seems to have decided that Abood must go. In his opinion in a 2012 case called Knox v. Service Employees International Union, he tackled an issue the case did not present: “[C]ompulsory fees constitute a form of compelled speech and association that imposes a ‘significant impingement on First Amendment rights,’” he wrote. “Our cases to date have tolerated this ‘impingement,’ and we do not revisit today whether the Court’s former cases have given adequate recognition to the critical First Amendment rights at stake.”
That is justice-speak for “Bring me a case.” By 2014, a candidate had appeared: Harris v. Quinn, a challenge to a “fair share” arrangement for home-health workers in Illinois who were paid by the state using Medicaid funds. Abood seemed doomed. But in the end, the Court couldn’t muster five votes to overturn Abood altogether; instead, the conservative majority held that the home-health workers weren’t “full-fledged” state workers at all. The union lost because Abood didn’t apply.
Someone on the Court’s right side—it’s not clear who—had gotten cold feet with Harris; but it seemed likely that, if a case dealing directly with public-employees unions could be gotten before the Court, that justice would fall into line. The anti-union Center for Individual Rights rushed into court in California on behalf of ten public-school teachers (precisely the same kind of workers as in Abood) who object to the fees.