They are helped by the fact that ICE agents cannot forcibly enter the homes of their targets under the law. But if past tactics are any measure, agents are likely to come to the operation armed with ruses to coax people outside. They will likely have new strategies that might help to counteract the preparations that undocumented immigrants have been making with the help of their lawyers.

Anticipating that they will not manage to block all of the arrests through preventive strategies, immigration lawyers and advocates across the country have been working swiftly to distribute contingency plans for those who are captured.

Shannon Camacho, a coordinator of the Los Angeles Raids Rapid Response Network for immigrants, said the organization is urging undocumented parents with children who are United States citizens or legal permanent residents to sign caregiver affidavits, so that if the parents are deported, the children will not be left without legal guardians.

“When people are arrested, their children can’t be picked up from school, or if they’re caring for the elderly, no one will be around to give them their medicine. We tell them to have designated people in their friends or family networks to respond,” said Ms. Camacho.

Mony Ruiz-Velasco, the director of PASO-West Suburban Action Project, a community group in Melrose Park, Ill., said her staff and volunteers were advising families to memorize at least one phone number so that they can call for help if they are detained.

Win, the largest nonprofit provider of shelters for families with children in New York, notified families with undocumented members to be cautious and to leave over the weekend, if necessary, a person familiar with the instructions confirmed. The nonprofit operates 11 shelters, and houses about 10 percent of the nearly 12,000 families in the city currently living in shelters.

A 17-year-old girl, who lives in one of the shelters and who spoke on the condition of anonymity, said a shelter employee used coded language to warn her family to go into hiding and to return on Monday. “They said, ‘Your room is going to be very hot this weekend. Come back Monday when things cool off,’” she said.