A 1940 law, the Alien Registration Act, requires all foreign nationals age 14 and older who will be in the U.S. for 30 days or more to register and be fingerprinted. Adults must always carry proof of registration, and noncompliance may result in fines, imprisonment, or removal proceedings. Although historically unenforced, the Trump administration began enforcing it on April 11, 2025, through a new online process using Form G-325R.

Those required to register include many noncitizens not previously documented, such as Canadians without Form I-94, undocumented immigrants, and children turning 14. Registration does not confer legal status and may expose individuals to legal risk, so consultation with an immigration attorney is advised. Certain groups, like lawful permanent residents and visa holders already registered, are exempt. Registration is completed online, followed by a biometrics appointment, and results in a digital proof of registration.