In Southern California, hundreds of people reporting for special registration at INS offices has been arrested and placed in detention. Estimates are that a minimum of 500 people have been arrested, and possibly as many as 1000. Most of those arrested are Iranian, but people from all countries subject to special registration have been arrested. The Los Angeles area is home to the largest Iranian population outside Iran, with about 600,000 Iranians living in the area.

The arrests have prompted numerous demonstrations by Islamic and immigrant groups, and the American Civil Liberties Union has compared the arrests to the detention of Japanese-Americans during World War Two. They are also concerned about the efficacy of arresting those people who are willing to appear for registration, observing that terrorists are unlikely to comply with the registration requirement. Many are also concerned that jail overcrowding in Southern California will mean that many of those arrested will be transferred to other states where they could languish in detention for months before receiving a hearing.

The INS has said that it will not release information on the number of people arrested, nor on the number of people who have appeared for special registration. The agency has said that the arrests were based on a number of charges, including visa overstays, criminal convictions, and other immigration violations. Most of those arrested have since been released on bail and ordered to appear before immigration judges for hearings.