The Department of Justice (DOJ) expanded the margin of action of the armed forces on the border with Mexico by determining that the military can detain people accused of entering the so-called National Defense Areas without authorization.
The measure is part of the immigration strategy of the Donald Trump administration, which has converted different stretches of the southern border into areas under the control of the Department of Defense.
According to the opinion of the Department of Justice's Office of Legal Counsel, soldiers can detain those who leave one of these areas before they are brought to the disposal of civil authorities for possible trespass crimes.
CBS News revealed that Deputy Attorney General William Hyde maintained in the document that this action does not contravene the Posse Comitatus Act, which limits the participation of the armed forces in law enforcement tasks within the United States.
“Using military personnel to arrest trespassers just outside a private security zone would not violate the Posse Comitatus Act,” Hyde said.
Six military zones on the border
The Trump administration has so far established six National Defense Areas in Arizona, California, New Mexico and Texas. Some cover considerable tracts of land that previously had no obvious appearance of military installations.
For this reason, the Pentagon has placed signs in English and Spanish to warn that these are restricted spaces and that unauthorized entry may lead to criminal consequences.
The information about the new legal criteria was reported based on the opinion of the Department of Justice and taken up by US media that follow immigration policy and military operations on the border.
The Justice Department began bringing charges related to these areas in April 2025. Allegations may include violations of military security regulations and unauthorized entry onto military property.
More than 20,000 soldiers deployed
The scope of the strategy comes as the Department of Defense maintains a sizable presence on the border. According to figures cited in the report, more than 20,000 military personnel have participated in border deployments during Trump's second term.
The Southern Border Joint Task Force currently has about 8,000 troops and has made 161 arrests within the National Defense Areas.
However, the Office of Legal Counsel's own opinion is advisory and does not establish judicial precedent. Its application could continue to raise questions about the boundaries between military functions and the application of civilian laws.
The expansion of these powers also occurs while crossings at the southern border remain at historically low levels. Border Patrol data cited in the report shows that apprehensions went from nearly 2 million in fiscal year 2023 to fewer than 240,000 in 2025.
