By Cass R. Sunstein

The Supreme Court has yet to decide this year’s attention-grabbing cases on same-sex marriage, affirmative action and the Voting Rights Act. But several days ago, a divided court decided Arlington v. FCC, an important victory for Barack Obama’s administration that will long define the relationship between federal agencies and federal courts.

The underlying question was this: If a law is ambiguous, who gets to interpret it? Federal judges or the agency that carries it out? Who interprets the crucial ambiguities in the Affordable Care Act, the Clean Air Act or the Wall Street Reform and Consumer Protection Act?

The divisions within the court defied the usual ideological predictions. In a powerful and convincing opinion by Justice Antonin Scalia, the court’s majority ruled that even when the agency is deciding on the scope of its own authority, it has the power to interpret ambiguities in the law. Scalia was joined by Justices Ruth Bader Ginsburg, Elena Kagan, Sonia Sotomayor and Clarence Thomas.

In an agitated dissent, Chief Justice John Roberts Jr., joined by Justices Samuel Alito and Anthony Kennedy, contended that the courts, not the agency, must decide on the scope of the agency’s power. (Justice Stephen Breyer wrote separately and only for himself.)

The court’s ruling, which involved the Federal Communications Commission’s defense of its rules governing siting applications for wireless facilities, is an important win for all future presidents, whether Republican or Democratic. It reduces confusion and uncertainty in the law. It also strengthens the hand of agencies carrying out Obama’s health-care law and financial reform.

Agencies’ power

To understand the decision, a little background will be helpful. For almost three decades, the court has ruled that when Congress gives a federal agency the power to issue regulations, that agency is usually authorized to interpret ambiguities in the original legislation.

Sometimes Congress speaks clearly. But in some cases, its meaning is obscure. For example, does the word “source” in the Clean Air Act mean each smokestack in a plant or the entire plant?

The court has ruled that the agency is entitled to interpret such ambiguities, as long as its interpretation is reasonable. The reasoning here is that by giving rule-making authority to agencies, Congress implicitly delegated interpretive power to them, as well.

The court has also noted that compared with the courts, the agencies are politically accountable and have technical expertise, so they are in the best position to resolve ambiguities.

Why the heated dispute in Arlington? For more than a decade, judges and scholars have differed over what happens when an agency is deciding on its own “jurisdiction,” that is, on the scope of its own authority. Imagine that the Food and Drug Administration is asserting its power over certain tobacco products, or the Department of Health and Human Services is applying an ambiguous provision of the Affordable Care Act to certain employers, or the Federal Communications Commission is trying to regulate some new technology. In such cases, shouldn’t a federal court, rather than the agency, get to interpret ambiguities?

In giving an affirmative answer, Roberts expressed concern about “the authority administrative agencies now hold over our economic, social and political activities,” and about a federal bureaucracy that “continues to grow.” He insisted that “the danger posed by the growing power of the administrative state cannot be dismissed.”

In these circumstances, Roberts argued that the court, and not the agency, must resolve ambiguities about the scope of the agency’s authority. Judges must “not leave it to the agency to decide when it is in charge.”

Scalia’s response

It is a forceful argument, and Roberts made it well, but Scalia offered a persuasive three-part response.

First, he invoked precedent, arguing that the court has long followed a general principle to the effect that “ambiguities will be resolved, within the bounds of reasonable interpretation, not by the courts but by the administering agency.”

Second, he contended that Roberts was quite wrong to say that courts could identify a separate category of cases—those involving the scope of an agency’s authority. The question is always whether the agency is acting within the bounds set by Congress. “There is no principled basis for carving out some arbitrary subset of cases,” he wrote. In his view, Roberts’ approach, forcing lower courts to draw ad hoc lines, would make the law unpredictable and produce chaos.

Third, Scalia insisted that the danger of agency overreaching is to be avoided, not by an arbitrary carve-out, but by requiring agencies to respect congressional limits on their authority.

A striking feature of the Arlington decision is the composition of the majority, with Scalia and Thomas joining Ginsburg, Kagan and Sotomayor.

What unified the court’s two leading conservatives and three of its more liberal justices? Scalia’s opinion reflects his longstanding commitment to clarity in the law, a commitment that Thomas shares. It also reflects the majority’s belief, cutting across ideological divisions, that ambiguities in the law should be resolved by officials who are ultimately accountable to the people and likely to be experts on the issues at hand.

Like Chief Justice Roberts, of course, many people are nervous about the power of administrative agencies, and the Arlington decision might well make them even more nervous. But would they really prefer ambiguities to be resolved by federal judges, who might have agendas of their own?

Scalia was right to identify the ultimate safeguard against administrative power: If Congress has clearly expressed its will, the matter is at an end. A potential benefit of the Arlington decision is to offer Congress an emphatic reminder of that fact.

Cass R. Sunstein, the Robert Walmsley university professor at Harvard Law School, is a Bloomberg View columnist. He is the former administrator of the White House Office of Information and Regulatory Affairs, the co-author of Nudge and author of Simpler: The Future of Government. The opinions expressed are his own.