What is Davis v. Michigan?

Davis v. Michigan, 489 U.S. 803 , is a case in the Supreme Court of the United States holding that states may not tax federal pensions if they exempt their own state pensions from taxation. In the 1930s, the federal and state governments began to charge income tax on salaries paid to each other's employees. However, reciprocal treatment was required under the doctrine of intergovernmental immunity. The Court's ruling extended the reciprocity to pensions, since they are a form of deferred compensation for services previously rendered by an employee.