In 1940, Congress passed the Alien Registration Act, also known as the Smith Act, in response to the growing threat of war in Europe and in Asia. Under the new law, all aliens in the United States age 14 and older were required to register and be fingerprinted. Japanese immigrants were included, of course, regardless of how long they had lived as permanent residents of the United States. Since Korea was under the control of Japan at this time, Korean immigrants were classified as subjects of Japan. Each immigrant was assigned an Alien Registration Number and given an Alien Registration Receipt Card that they were required to carry at all times.
This was the first time all resident aliens were required to be registered, fingerprinted, and were now required to inform the government of any changes of address. The first immigrant group required to register and carry documentation of their registration was Chinese immigrants. In 1892, the Geary Act extended the Chinese Exclusion Act for another 10 years and required that all Chinese immigrants register and carry their documentation with them at all times. In 1928, all new immigrants were given identity cards upon entry, but no attempt was made at that time to force all aliens in residence to register or carry identification until the Smith Act was passed in 1940.
The immediate purpose of the Act was to strengthen U.S. security in a time of growing conflict in Europe and Asia. Registration was done at post offices instead of police stations to avoid the implication that this was a criminal process and to alleviate fears that registration might be a strategy to lure aliens to register so that they could be deported. As a result of this act, nearly five million aliens were registered, which was a higher number than originally expected. Francis Biddle , who at the time was Solicitor General, was uneasy with the Act, arguing that the law would exaggerate the estrangement of aliens in the country. In his memoir, In Brief Authority , Biddle wrote that the enforcement of this Act this would mark the beginning of a witch hunt. Some of the unintended results of alien registration were when cities began purging aliens from their relief rolls, and across the country aliens were denied charity and fired from employment. 
For More Information
Biddle, Francis. In Brief Authority. New York: Doubleday & Company, Inc., 1962.
Daniels, Roger. The Japanese American Cases: The Rule of Law in Time of War. Lawrence: University Press of Kansas, 2013.
Harrison, Scott. " Alien Registration Act of 1940 ." Framework. Los Angeles Times, February 14, 2012.
Lee, Erika. At America's Gates: Chinese Immigration During the Exclusion Era, 1882-1943. Chapel Hill: University of North Carolina Press, 2003.
Russell, Jan Jarboe. The Train to Crystal City: FDR's Secret Prisoner Exchange Program and America's Only Family Internment Camp During World War II. New York: Scribner, 2015.
- Jan Jarboe Russell, The Train to Crystal City (New York: Scribner, 2015), 47-49; Francis Biddle, In Brief Authority (New York: Doubleday & Company, Inc., 1962), 110; Jerre Manginone, An Ethnic at Large (New York: G.P. Putnam's Sons, 2001), 271.