Most states limit some benefits, such as welfare payments or free medical care for indigents, to state residents; all states limit voting to residents. Legislative classifications based on nonresidence or out-of-state citizenship are not subjected to heightened judicial scrutiny under the equal protection clause, and these residence requirements consistently pass the relaxed rational basis test.
Because state citizenship and residence are "essentially interchangeable" for purposes of the privileges and immunities clause of Article IV, however, discriminations against nonresidents are scrutinized more carefully under that provision. The state must justify such discriminations by showing that they are substantially related to dealing with some special problem or condition caused by nonresidents. A state might constitutionally charge out-ofstaters more than residents for a license to cut timber, if the increased charge bore some fair relation to increased costs of enforcing conservation laws against nonresidents. Similarly, nonresidents might constitutionally be denied welfare benefits or charged higher tuition for attending a state university, because residents have supported the welfare system and the university out of general tax revenues. The notion of a "political community" justifies limiting the vote to residents.
Discriminations not so justified, however, violate Article IV's privileges and immunities clause when they touch privileges that are deemed "fundamental" to interstate harmony. (See toomer v. witsell, 1948, commercial shrimping; hicklin v. orbeck, 1978, employment; doe v. bolton, 1973, abortion; new hampshire supreme court v. piper, 1985, practice of law.)
Requirements of residence for a specified period raise an additional constitutional problem. The Court has invalidated a number of these durational residence requirements on equal protection grounds, also invoking the right to travel or migrate interstate. (See shapiro v. thompson, 1969, welfare benefits; dunn v. blumstein, 1972, one-year requirement for voting invalid; later decisions allow fifty-day residence qualification; Memorial Hospital v. Maricopa County, 1974, nonemergency medical care for indigents; Zobel v. Williams, 1982, payment of bonuses apportioned to length of residence in the state. But see sosna v. iowa, 1975, one year's residence a valid requirement for access to divorce court.) William Cohen has argued persuasively that these decisions are consistent with a theory that validates a state's durational residence requirement only when the requirement is a reasonable test of a newcomer's intent to remain a resident of the state. The Supreme Court has not yet embraced this theory—or, indeed, any coherent theory explaining its decisions concerning durational residence requirements.
Kenneth L. Karst
Cohen, William 1984 Equal Treatment for Newcomers: The Core Meaning of National and State Citizenship. Constitutional Commentary 1:9–19.
Varat, Jonathan D. 1984 "Citizenship" and Interstate Equality. University of Chicago Law Review 48:487–572.