Pennsylvania Coal Co v Mahon

Pennsylvania Coal Co v Mahon is a 1922 decision of the United States Supreme Court, written by Justice Oliver Wendell Holmes, that created the modern doctrine of regulatory takings. Pennsylvanias Kohler Act barred coal mining that would cause the ground above to subside, which effectively nullified a mining right the coal company had specifically bargained for and retained by deed. The Supreme Court held that while property may be regulated to a certain extent, a regulation that goes too far in destroying the value of a property right is the equivalent of a taking of property, requiring just compensation under the Fifth Amendment even though the state never physically occupied the land. The case remains the origin point for the ongoing constitutional question of when regulation becomes a compensable taking.