THE labour movement in America has seen better days. In the 1960s, about a third of American workers were union members. Today, with “right-to-work” laws in place in 25 states, the figure hovers at 10%. In June, when the Supreme Court issues a decision in Friedrichs v California Teachers Association, the decline may well accelerate. Rebecca Friedrichs, a public-school teacher in California who left a union she disagreed with, is challenging a rule that says non-members must pay “fair-share fees” to cover the costs of collective bargaining. It violates the First Amendment right to freedom of speech, she and nine other teachers say, to be forced to subsidise an organisation whose politics they reject. Since unions form an important part of the Democratic coalition, the ruling will resonate beyond the world of union members and their bosses.

In 1977, in Abood v Detroit Board of Education, the court ruled that while unions could not charge non-members for political activities, states could allow unions to collect compulsory fees to support negotiations over workplace matters like wages and benefits. In oral arguments on January 11th Michael Carvin, the plaintiffs’ lawyer, argued that negotiating teachers’ contracts is an essentially political endeavour, because they involve controversial questions of “public concern”. The fair-share or “agency fee” model forces his clients to espouse an “ideological viewpoint which they oppose”, and violates “basic speech and association rights”.

The tenor of the hearing suggested that a majority of the justices are keen to abandon Abood and end the mandatory fees—freeing Ms Friedrichs and millions of public-sector workers from the duty of writing cheques to the unions who negotiate on their behalf. Justice Samuel Alito sent strong hints of this willingness in two recent cases, calling Abood “something of an anomaly” in 2012. This view earned the apparent endorsement of Justice Anthony Kennedy, who noted that, under the current regime, teachers who oppose seniority-based salaries must nevertheless fund a union’s “public-relations campaign to protest merit pay”. It “makes no sense”, Justice Kennedy complained, to tell teachers who “strongly, strongly disagree with the union position on teacher tenure, on merit pay, on merit promotion, on classroom size” that they must pay to support those positions but are otherwise “free to go out and argue against” them.

The defence of Abood by the court’s left wing had the ring of a somewhat desperate rearguard action. Justice Stephen Breyer suggested that the plaintiff’s complaint is “pretty far removed from the heart of the First Amendment”, since employees “can say what they want” outside the bargaining room. For Justice Elena Kagan, the disgruntled teachers have a “heavy burden” in “ask[ing] us to overrule a decision” as “there are tens of thousands of contracts with these [agency-fee] provisions” affecting “millions of employees”. Justice Breyer wondered “what happens to the country thinking of us as a kind of stability” if the court votes to “overrule a compromise that was worked out over 40 years”.

That point may have been designed to appeal to Chief Justice John Roberts who, according to Elizabeth Wydra of the Constitutional Accountability Centre, “cares about the public’s perception of the court and does not want it to be seen as an institution easily swayed by changing political winds”. But if Mr Roberts is to be the fifth vote to save agency fees, he masked that well. Allocations to public education always compete with other budget areas such as “public housing [and] welfare benefits”, he said. “It’s all money.”

What would happen if agency fees disappear? The unions, along with a host of agency-shop states, including California, argue that their membership rolls would thin and finances would wither. This is not necessarily the case: several European countries with higher rates of union membership than America do not allow unions to compel non-members to pay dues. Even if the ruling against California Teachers did accelerate the decline of unions, that would not necessarily be bad for Democrats. Unions can exercise a disproportionate influence on candidate selection, particularly in House and statehouse races. A party in which they had less influence might succeed in adopting more popular positions on subjects like merit pay and charter schools. In the long run, those alarming right-wing justices may just end up doing the left a favour.