The Non-Detention Act of 1971 was passed to repeal portions of McCarran Internal Security Act of 1950, specifically Title II, the "Emergency Detention Act". It had allowed for detention of suspected subversives without the normal Constitutional checks required for imprisonment. The Non-Detention Act requires specific Congressional authorization for such detention. Passed as Public Law 92-128, 85 Stat. 347 (1971), it was codified at 18 U.S.C. § 4001(a).
§ 4001. Limitation on detention
(a) No citizen shall be imprisoned or otherwise detained by the United States except pursuant to an Act of Congress.
In recent years, the statute has been used to challenge military detainment of U.S. citizens accused of terrorist activity. A Congressional Research Service report on the history of the Non-Detention Act concluded,
Legislative debate, committee reports, and the political context of 1971 indicate that when Congress enacted Section 4001(a) it intended the statutory language to restrict all detentions by the executive branch, not merely those by the Attorney General. Lawmakers, both supporters and opponents of Section 4001(a), recognized that it would restrict the President and military authorities.
The Supreme Court of the United States originally took the case of Rumsfeld v. Padilla to decide the question of whether Congress's Authorization for Use of Military Force authorized the President to detain a U.S. citizen, but did not give an answer, instead ruling that the case had been improperly filed.
See also 
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