Whether a regulatory act constitutes a taking requiring compensation depends on the extent of diminution in the value of the property. Decided December 11, 1922 (argued November 14, 1922). Opinion of the Court: Oliver Wendell Holmes → go there Dissenting: Brandeis. Applied: the Fifth Amendment → go there Applied: the Fourteenth Amendment → go there Topic: Takings Clause. Pennsylvania Coal Co. v. Mahon, 260 U.S. 393 (1922), was a case in which the Supreme Court of the United States held that whether a regulatory act constitutes a taking requiring compensation depends on the extent of diminution in the value of the property. Wiki link