"immigrant" (documented or undocumented) is part of the federal law. That would include green card holders since they are immigrant's.
Found it.......
Federal law requires that men who are at least 18 years old, but not yet 26 years old, must be registered with Selective Service. This includes all male non-citizens within these age limits who
permanently reside in the United States. Men with "
Green Cards" (lawful permanent residents) must register. Men living in the United States without USCIS documentation (undocumented aliens) must also register. But men cannot register after reaching age 26.
A male non-citizen who first enters the U.S. as a permanent resident after he has already passed his 26th birthday is not required to register because he is over the age limit. Non-immigrant men who are in the U.S. temporarily (diplomatic corps, trade mission personnel, men holding valid visitor or student visas, etc.) do not register. Women do not register because the law does not apply to them.