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| Long title | An act making appropriations for the support of the Army for the fiscal year ending June thirtieth, eighteen hundred and seventy-nine, and for other purposes. |
| Nicknames | Army Appropriations Act of 1878 |
| Enacted by | the45th United States Congress |
| Effective | June 18, 1878 |
| Citations | |
| Public law | Pub. L. 45–263 |
| Statutes at Large | 20 Stat. 145a.k.a. 20 Stat. 152 |
| Codification | |
| U.S.C. sections created | 18 U.S.C. § 1385 |
| Legislative history | |
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| Major amendments | |
| 1956, 1981, 2021 | |
ThePosse Comitatus Act is aUnited States federal law (18 U.S.C. § 1385, original at 20 Stat. 152) signed into law on June 18, 1878, byPresidentRutherford B. Hayes that limits the use offederal military personnel to enforce domestic law by thefederal government or by other government entities such as county sheriffs and justices of the peace. Congress passed the Act as an amendment to an armyappropriations bill following the end ofReconstruction and updated it in 1956, 1981 and 2021.
The Act originally applied only to theUnited States Army, but a subsequent amendment in 1956 expanded its scope to theUnited States Air Force. In 2021, theNational Defense Authorization Act for Fiscal Year 2022 further expanded the scope of the Act to cover theUnited States Navy,Marine Corps, andSpace Force. The Act does not prevent theArmy National Guard or theAir National Guard understate authority from acting in alaw enforcement capacity within its home state or in an adjacent state if invited by that state's governor. TheUnited States Coast Guard (under theDepartment of Homeland Security) is not covered by the Act either, primarily because although it is anarmed service, it also has amaritime law enforcement mission.
The title of the Act comes from the legal concept ofposse comitatus, the authority under which acounty sheriff, or another law officer, can conscript any able-bodied person or group to assist in keeping the peace.
The Act, § 15 of the appropriations bill for the Army for 1879 (found at 20 Stat. 152) was a response to, and subsequent prohibition of, themilitary occupation of the formerConfederate States by theUnited States Army during the twelve years ofReconstruction (1865–1877) following theAmerican Civil War (1861–1865).
TheU.S. Constitution places primary responsibility for the holding ofelections in the hands of the individual states.[1] The maintenance of peace, conduct of orderly elections, and prosecution of unlawful actions are all state responsibilities, according to any state's role of exercising police power and maintaining law and order, whether part of a wider federation or a unitary state.[2] However, in the former Confederate States, many paramilitary groups sought to suppress, often through intimidation and violence, African-American political power and return the South to rule by the predominantly white Democratic Party. Although African Americans were initially supported by the federal government, as Reconstruction went on, that support waned.[3] Following the bitterly disputed1876 U.S. presidential election andCompromise of 1877,Congressmen andSenators from the former Confederate States returned to Washington and prioritized prohibiting the federal government from reimposing control over their states.[4] After President Hayes used federal troops to end theGreat Railroad Strike of 1877, there was sufficient bipartisan support to pass what became the Posse Comitatus Act.[5][6][4]
The original Posse Comitatus Act referred exclusively to the United States Army. TheAir Force, established during the 20th century initially as a branch of the Army, was added in 1956. TheNavy andMarine Corps were not mentioned in the Act but were subject to the same restrictions byDepartment of Defense regulation until their inclusion in the act in 2021.[4][7] The Space Force, established in 2020, was also included in the Act in 2021. TheUnited States Coast Guard is not included in the act even though it is part of the six armed services as it is explicitly given federal law enforcement authority onmaritime law.[8] The modern Coast Guard did not exist at the time the Act became law in 1878. Its predecessor, theUnited States Revenue Cutter Service, was primarily a customs enforcement agency and part of theUnited States Department of the Treasury.[9] In 1915, when the Revenue Cutter Service and theUnited States Lifesaving Service were amalgamated to form the Coast Guard, the service was both made a military branch and given federal law enforcement authority.
In the mid-20th century, the administration of PresidentDwight D. Eisenhower used an exception to the Posse Comitatus Act, derived from theEnforcement Acts, to send federal troops intoLittle Rock, Arkansas, during the1957 school desegregation crisis. The Arkansas governor had opposed desegregation after theUnited States Supreme Court ruled in 1954 inBrown v. Board of Education that segregated public schools were unconstitutional. The Enforcement Acts, among other powers, allowed the president to call up military forces when state authorities were either unable or unwilling to suppress violence that was in opposition to the citizens' constitutional rights.[10]
In the summer of 2020, theGeorge Floyd protests in Washington, D.C. generated controversy when National Guard troops were called in to suppress protests without PresidentDonald Trump's invoking theInsurrection Act (though he threatened to do so). One set of troops, theDistrict of Columbia National Guard, has historically operated as the equivalent of a state militia (under Title 32 of theUnited States Code) not subject to Posse Comitatus Act restrictions, even though it is a federal entity under the command of the President and the Secretary of the Army.[11] National Guard troops from cooperative states were also called in at the request of federal agencies, some of whom were deputized as police.[12] Attorney GeneralWilliam Barr cited32 U.S.C. § 502(f)(2)(a),[12] which says National Guard troops may engage in "support of operations or missions undertaken by the member's unit at the request of the President or Secretary of Defense." Saying the intent of §502 (titled "Required drills and field exercises") was to cover training exercises only, SenatorTom Udall and U.S. RepresentativeJim McGovern described this as a "loophole" to circumvent Posse Comitatus Act restrictions, and introduced legislation to close it.[13]
In 2020, U.S. RepresentativeAdam Schiff introduced an amendment to the Act to expand its coverage to include the U.S. Navy, Marine Corps, and Space Force.[14] This amendment was eventually included in the 2022 National Defense Authorization Act.[15]
The 2025 lawsuitNewsom v. Trump raised constitutional and statutory challenges under the Posse Comitatus Act in response to the domestic deployment of U.S. Marines and National Guard troops in California.[16] On September 2, 2025, federal judgeCharles Breyer ruled that the federal deployment of the National Guard in California violated the Posse Comitatus Act and issued an injunction against it.[17]
The original provision of 1878 was enacted as Section 15 of chapter 263, of the Acts of the 2nd session of the45th Congress.
Sec. 15. From and after the passage of this act it shall not be lawful to employ any part of the Army of the United States, as a posse comitatus, or otherwise, for the purpose of executing the laws, except in such cases and under such circumstances as such employment of said force may be expressly authorized by the Constitution or by act of Congress; and no money appropriated by this act shall be used to pay any of the expenses incurred in the employment of any troops in violation of this section and any person willfully violating the provisions of this section shall be deemed guilty of a misdemeanor and on conviction thereof shall be punished by fine not exceeding ten thousand dollars or imprisonment not exceeding two years or by both such fine and imprisonment.[18]
The text of the relevant legislation following its amendment in 2021 is as follows:
18 U.S.C. § 1385. Use of Army, Navy, Marine Corps, Air Force, and Space Force as posse comitatus:Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army, the Navy, the Marine Corps, the Air Force, or the Space Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.
Also notable is the following provision withinTitle 10 of the United States Code (which concerns generally the organization and regulation of the armed forces and Department of Defense):
10 U.S.C. § 275. Restriction on direct participation by military personnelTheSecretary of Defense shall prescribe such regulations as may be necessary to ensure that any activity (including the provision of any equipment or facility or the assignment or detail of any personnel) under this chapter does not include or permit direct participation by a member of the Army, Navy, Air Force, or Marine Corps in a search, seizure, arrest, or other similar activity unless participation in such activity by such member is otherwise authorized by law.
In 2006, Congress modified theInsurrection Act as part of the2007 Defense Authorization Bill (repealed as of 2008). On September 26, 2006, PresidentGeorge W. Bush urged Congress to consider revising federal laws so that U.S. armed forces could restore public order and enforce laws in the aftermath of anatural disaster, terrorist attack or incident, or other condition.These changes were included in theJohn Warner National Defense Authorization Act for Fiscal Year 2007 (H.R. 5122), which was signed into law on October 17, 2006.[19]
Section 1076 is titled "Use of the Armed Forces in major public emergencies". It provided that:
The President may employ the armed forces ... to ... restore public order and enforce the laws of the United States when, as a result of a natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition ... the President determines that ... domestic violence has occurred to such an extent that the constituted authorities of the State or possession are incapable of maintaining public order ... or [to] suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy if such ... a condition ... so hinders the execution of the laws ... that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law ... or opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.[20]
In 2008, these changes in the Insurrection Act of 1807 wererepealed in their entirety, reverting to the previous wording of the Insurrection Act.[21] It was initially written to limit presidential power as much as possible in the event of insurrection, rebellion, or lawlessness.
There are several situations in which the Act does not apply. These include:
Although it is an armed service,[23] the U.S. Coast Guard, which operates under theUnited States Department of Homeland Security during peacetime, is not restricted by the Posse Comitatus Act and has explicit authority to enforce federal law. This is true even when the Coast Guard operates as a service within theUnited States Navy during wartime.[9]
In December 1981, theMilitary Cooperation with Civilian Law Enforcement Agencies Act was enacted, clarifying permissible military assistance to domestic law enforcement agencies and the Coast Guard, especially in combatingdrug smuggling into the United States. Posse Comitatus clarifications emphasize supportive and technical assistance (such as the use of facilities, vessels, and aircraft, as well as intelligence support, technological aid, and surveillance) while generally prohibiting direct participation of U.S. military personnel in law enforcement (such as search, seizure, and arrests). For example, a U.S. Navy vessel may be used to track, follow, and stop a vessel suspected of drug smuggling, but Coast GuardLaw Enforcement Detachments (LEDETs) embarked aboard the Navy vessel would perform the actual boarding and, if needed, arrest the suspect vessel's crew.[9]
Federal troops have a long history of domestic roles, including occupying secessionist Southern states during Reconstruction and putting down major urban riots. The Posse Comitatus Act prohibits using active duty personnel to "execute the laws"; however, there is disagreement over whether this language may apply to troops used in an advisory, support, disaster response, or other homeland defense role, as opposed to domestic law enforcement.[2]
On March 10, 2009, members of theU.S. Army Military Police Corps fromFort Rucker were deployed toSamson, Alabama, in response toa shooting spree. Samson officials confirmed that the soldiers assisted in traffic control and securing the crime scene. Thegovernor of Alabama did not request military assistance, nor did PresidentBarack Obama authorize their deployment. Subsequent investigation found that the Posse Comitatus Act was violated and several military members received "administrative actions".[24][25]
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