The purpose is to speed up the deportation of members of the Venezuelan cartel Tren de Aragua, which Trump claims has "infiltrated" the country.
Shortly after the president's proclamation, a federal judge decided to temporarily stop the deportations for 14 days or until he has considered whether the measure is legal.
The law, Alien Enemies Act, was last used by President Franklin D Roosevelt during World War II to intern and deport non-citizens of, among others, Japanese and German origin.
Since it is designed to be invoked when the US is at war or threatened by invasion, experts believe it will meet resistance in American courts, reports CNN.
The White House can appeal the judge's temporary stop by Monday.
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