Four young Nisei carried the constitutional challenge. Minoru Yasui, a lawyer, walked a Portland street after curfew to force his own arrest and spent nine months in solitary confinement; Gordon Hirabayashi, a Quaker student, refused both curfew and removal as a matter of conscience; Fred Korematsu simply declined to report and was convicted of remaining in his own home town; Mitsuye Endo, a state employee of unquestioned loyalty, petitioned for habeas corpus from inside the camps. The Supreme Court upheld the curfew in 1943 and, in Korematsu v. United States (1944), the exclusion itself — over Justice Jackson's warning that the ruling lay about "like a loaded weapon."

Ex parte Endo, decided the same day as Korematsu, held that the government could not detain a concededly loyal citizen, forcing the camps' closure. Four decades later, historians found the wartime solicitor general had suppressed intelligence reports contradicting the military's claims; federal courts vacated the convictions of Korematsu (1983), Yasui, and Hirabayashi (1987) on writs of coram nobis. All three received the Presidential Medal of Freedom, and in 2018 the Supreme Court declared that "Korematsu was gravely wrong the day it was decided."