The planned arrests are a departure for ICE agents, who typically focus on deporting individual adults, particularly those with criminal records, rather than targeting families with children. Federal immigration authorities said they hoped to sweep up at least 2,000 undocumented migrants across the country.

Raids targeting migrant families have happened before, and have been known to escalate into emotional scenes. But officials at the Department of Homeland Security who have discussed the operations with reporters in recent weeks said that they were intended to deter migration, with the hope that images of children and parents being hauled out of their homes would discourage others from entering the United States.

Democratic-led state and local governments have already been mobilizing in opposition of the raids. On Wednesday, Mayor Lori Lightfoot of Chicago announced that she had permanently banned ICE from gaining access to the city police department’s digital records, and said the Chicago police would not in any way assist with the immigration sweep.

“The threat of raids has forced our residents to hide in the shadows, living in constant fear and not going to school or work,” she said at a news conference. “I’ve personally spoken with ICE leadership in Chicago and voiced my strong objection to any raids and the things that are happening that are terrorizing and traumatizing our community.”

Gov. Gavin Newsom of California posted a video on Thursday on Twitter advising migrants living in California on how to avoid arrest.

“We have your back,” he said in the video. “I just want to say to folks who are anxious about a knock on the door, no abras la puerta. You don’t have to open the door. Without a warrant, you don’t have to open the door.”

Four nonprofit groups represented by the American Civil Liberties Union filed a lawsuit in New York seeking a court order blocking the operation. In the lawsuit, the lawyers claim that many of the migrants failed to appear for their scheduled appearances in immigration court because border agency officials failed to inform them of their court dates.