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.

In 1921, the Commonwealth of Pennsylvania passed the Kohler Act, which prohibited the mining of anthracite coal in such way as to cause the subsidence of, among other things, any structure used as a human habitation.

The Supreme Court of Pennsylvania reversed, holding that the statute was a, "legitimate exercise of the police power" and granted an injunction.

The Court ruled that whether a regulatory act constitutes a taking requiring compensation depends on the extent of diminution in the value of the property.

(2) The statute, in general, purports to extinguish the mining rights to valuable properties under surfaces owned by the public and the government.

Today, the Supreme Court quotes Justice Holmes in Mahon for the recognition of the invalidity of a government regulation that so severely burdens private property that it constitutes a taking under the Fifth Amendment.

Yet a brief submitted for the city of Scranton "painted a picture of disaster, which has been accepted as the likely outcome of the decision in the legal literature.

In their study of the anthracite saga, The Kingdom of Coal (1985), the historians Donald Miller and Richard Sharpless did not mention subsidence in the 360 pages" of their book.

[12] When Fischel visited the Anthracite Heritage Museum near Scranton, he asked the librarian to help him locate works on subsidence and, "all that was available were technical pamphlets and a few relatively recent (post 1950) newspaper clippings that illustrated some damage.

[14] Benjamin Barros[15] noted that Justice Holmes, throughout his career as a state and federal judge, "held a consistent view ... that restrictions imposed through the police power could reach a point where they become takings and violate the Just Compensation Clause.

[17] In fact, in a letter dated January 13, 1923, Justice Holmes stated "I always have thought that old Harlan's decision in Mugler v. Kansas was pretty fishy.