In general, individual states have the power to make quarantine decisions affecting movements within their borders, pursuant to the Tenth Amendment to the Constitution, which leaves to the states “the powers not delegated to the United States.” Such residual powers include what’s generically known as the “police power”—that is, the power to establish laws protecting the health, safety, and welfare of the public. Every state has laws on the books permitting authorities—sometimes the governor, sometimes public health officials, sometimes both—to enact and enforce quarantine and isolation.
Meanwhile, the federal government derives its constitutional authority to quarantine people from the Commerce Clause, which gives Congress the power “to regulate Commerce with foreign Nations, and among the several States.” Thus, the federal government’s quarantine power applies most clearly at the U.S. border and for purposes of preventing the movement of infected people from state to state.
Under its Commerce Clause authority, Congress in 1944 passed the Public Health Service Act, which gave the executive branch power to enforce quarantines. The statute remains in effect today, although it has been amended several times, and although the relevant executive-branch agencies have been repeatedly reorganized and renamed. As it reads now, it gives the surgeon general, with the approval of the secretary of health and human services, the authority to take steps “necessary to prevent the introduction, transmission, or spread of communicable diseases from foreign countries into the States or possessions, or from one State or possession into another State or possession.” The statute also allows the president, via executive order and upon the recommendation of the HHS secretary, to issue regulations that “provide for the apprehension, detention, or conditional release of individuals . . . for the purpose of preventing” the spread of disease.