What they ruled: Judges no longer have to defer to agency officials when interpreting ambiguous federal statutes about the environment, the workplace, public health, and other aspects of American life.

Why it matters: In issuing its ruling, the court overturned a 40-year-old legal precedent known as “Chevron deference,” long a target of conservatives interested in reining in the power of the administrative state.

The Court’s 1984 decision in Chevron USA, Inc. v. Natural Resources Defense Council, Inc., established a foundational doctrine where courts should defer to reasonable agency interpretations of acts of Congress.  

 The court’s decision will significantly curtail the power federal agencies have to regulate thousands of private companies, products, industries and the environment.

Environmentalist organizations criticized the decision. The Southern Environmental Law Center issued a statement saying the ruling "shifts power to judges who do not have the expertise of agency staff who live and breathe the science, financial principles, and safety concerns that federal agencies specialize in". Vickie Patton of the Environmental Defense Fund warned that the decision “undermines vital protections for the American people at the behest of powerful polluters”. The Nation's Elie Mystal wrote that the decision was "the biggest judicial power grab since 1803", as it can strip power given by Congress to the experts in the appropriate field of the executive branch and place it in the hands of the judiciary for agencies such as the Environmental Protection Agency, the Security and Exchange Commission, and the Occupational Safety and Health Administration.