Native Americans were granted citizenship in a piece-meal manner until the Indian Citizenship Act of 1924, which unilaterally bestowed on them blanket citizenship status, whether they belonged to a federally recognized tribe or not, though by that date two-thirds of Native Americans had already become US citizens by various means. The Act was not retroactive, so that citizenship did not extend to Native Americans born before the effective date of the 1924 Act, or outside of the United States as an indigenous person. Even Native Americans who gained citizenship under the 1924 Act were not guaranteed voting rights until 1948. According to a survey by the Department of Interior, seven states still refused to grant Indians voting rights in 1938. Discrepancies between federal and state control provided loopholes in the Act's enforcement. States justified discrimination based on state statutes and constitutions. Three main arguments for Indian voting exclusion were Indian exemption from real estate taxes, maintenance of tribal affiliation and the notion that Indians were under guardianship, or lived on lands controlled by federal trusteeship. By 1947, all states with large Indian populations, except Arizona and New Mexico, had extended voting rights to Native Americans who qualified under the 1924 Act. Finally, in 1948, a judicial decision forced the remaining states to withdraw their prohibition on Indian voting.