The Pennsylvania Coal Company v. Mahon et al., 1922, is a landmark case in United States property law that established the regulatory taking doctrine. The dispute arose when the Pennsylvania Coal Company sold surface rights to a piece of land but retained mining rights underneath it, with an explicit warning of potential subsidence (sinking) due to mining activities. When the Kohler Act was passed prohibiting coal mining that caused subsidence under residential buildings, homeowner Mahon sued for enforcement as his house was on such land. The Supreme Court ruled in favor of the coal company stating that while government has inherent power to regulate private property use through its police powers without compensation, if regulation goes too far and effectively destroys or diminishes its economic value then it constitutes a 'taking' which requires just compensation under Fifth Amendment's Takings Clause. This decision marked an important shift towards protecting commercial interests from certain types of regulatory action.

In the dissenting opinion for Pennsylvania Coal Company v. Mahon, Justice Louis Brandeis argued that the state's interest in preventing subsidence outweighed any potential harm to private property rights. He contended that while it was true that a regulation which goes too far becomes a taking, he did not believe this particular law crossed such boundary. Instead, he saw it as an exercise of police power necessary to prevent public nuisance and protect public safety - both legitimate interests of the state. Furthermore, Justice Brandeis emphasized that every restriction upon use diminishes value but does not constitute a taking requiring compensation under Fifth Amendment; otherwise all zoning laws would be unconstitutional takings since they invariably decrease certain uses and hence values of properties affected by them.