Rebecca Friedrichs, an Orange County, Calif., teacher, is the lead plaintiff in a case coming before the U.S. Supreme Court on Jan. 11. (Greg Schneider/Associated Press)

REBECCA FRIEDRICHS and nine other California teachers are not all wrong in their critique of the oversized influence and self-interest of teachers unions. The unions have helped persuade society to value the vital role teachers play. But they also have become an often-reactionary force, opposing reforms that are especially important to poor and minority children. Public education — and many teachers — have been ill served by seniority rules that force administrators to lay off promising teachers instead of ineffective tenured ones. Students suffer from workplace rules that make it nearly impossible to fire a certifiably bad teacher or experiment with new types of schooling. Taxpayers have to bear the costs of teacher pensions that may be excessive, sometimes at the expense of other community needs.

But as much as we agree about the harm that’s been done to public education and, in particular, to children at risk, we don’t think the answer is for the Supreme Court to give relief by overturning settled law. Unions have contributed positively in many places; their policies can be democratically influenced by their members; and their proper role should be decided politically, not in a Supreme Court decision that would inevitably be seen as favoring one party over the other, since unions have been the traditional allies of Democrats.

Ms. Friedrichs, a teacher for 28 years who works in an elementary school near Anaheim, is lead plaintiff in a case set for oral arguments Monday. It is being closely watched because of its potential to upend the public labor sector. Friedrichs v. California Teachers Association seeks to strike down the requirement of California and more than 20 other states that public employees fund the union that bargains on their behalf even if they aren’t members of the union.

The court is being asked to overrule its 1977 precedent in Abood v. Detroit Board of Education authorizing states to require workers who are not union members to pay so-called agency fees — the portion of union dues that go for collective bargaining. That decision held that workers were not required to join unions or fund their political activities. But the Friedrichs plaintiffs argue that collective bargaining in the public sector, even on pay and conditions, is by definition political. By forcing them to pay for bargaining objectives they do not support, the law is therefore violating their First Amendment rights, they say.

Recent decisions of the court headed by Chief Justice John G. Roberts Jr. suggest there may be an appetite among some justices to overturn the system, but Abood has been reaffirmed numerous times, and its principles are entrenched in labor relations. The logic is that all teachers benefit when, for example, pay is increased, and the law shouldn’t allow free riders to reap those benefits without sharing in the costs of achieving them. It seems to us that the court is really being asked to decide whether public employee unions have become too powerful and need to be reined in. It’s a question worth debate. But it is more of a political than a constitutional issue, best answered on the state and local levels by voters and the people they elect.