Brushaber v. Union Pacific Railroad Co.
Chief Justice White’s opinion held that the Sixteenth Amendment created no new taxing power; it removed the apportionment requirement from a category of taxes the Court characterized as excises. The decision did the substantive work of reconciling Pollock with the Amendment without overruling Pollock.
The case is regularly cited by both the alternate-tax community (who sometimes overstate its limiting force) and the establishment (who treat the characterization as merely formal). The actual opinion is more interesting than either reading suggests, and rewards careful reading of the original text.