Chevron is unconstitutional for several reasons. It gives judicial power—the power to interpret the meaning of the law—to the administrative state within the Executive Branch. The Constitution, however, grants all judicial power to the Judicial Branch. Chevron is also unconstitutional because it biases the courts towards the agencies, stripping the judiciary of impartiality and denying litigants basic due process. But a third reason, and the focus of our brief, is that Chevron deference is ahistorical, arising not out of the original understanding of the Constitution but rather out of the administrative bloat of the New Deal era.
https://www.cato.org/blog/supreme-court-should-end-chevron-deference