Large-scale arrests outside immigration courts have unleashed fear among asylum-seekers and immigrants who are accustomed to remaining free while judges grind through a backlog of 3.6 million cases.

Migrants are being detained by immigration agents in courthouse hallways nationwide, sometimes moments after pleading their cases, raising alarm among attorneys and advocates.

A hearing on Tuesday at immigration court in Van Nuys, Calif., was supposed to be routine for a young family from Colombia, the first step in what they hoped would be a successful bid for asylum.