Federal Instrumentality Doctrine
The Army & Air Force Exchange Service is a federal instrumentality of the Department of Defense. Under the U.S. Constitution's Supremacy Clause and federal law codified at 10 U.S.C. § 2481, state and local governments cannot impose taxes on federal entities or their operations. Because every Exchange transaction is an activity of a federal agency, no state sales tax applies.
This is the same legal principle that prevents states from taxing federal buildings, military bases, or post offices. The Exchange is not receiving a special exemption — it is inherently exempt because it is part of the federal government. This distinction matters because it means the tax-free benefit cannot be revoked by state legislatures, governors, or local tax authorities. Only Congress could change this, and the Exchange system has operated tax-free for over 130 years.