Nationwide raids to arrest thousands of members of undocumented families have been scheduled to begin Sunday, according to two current and one former homeland security officials, moving forward with a rapidly changing operation, the final details of which remain in flux. The operation, backed by President Trump, had been postponed, partly because of resistance among officials at his own immigration agency.

The raids, which will be conducted by Immigration and Customs Enforcement over multiple days, will include “collateral” deportations, according to the officials, who spoke on the condition of anonymity because of the preliminary stage of the operation. In those deportations, the authorities might detain immigrants who happened to be on the scene, even though they were not targets of the raids.

When possible, family members who are arrested together will be held in family detention centers in Texas and Pennsylvania. But because of space limitations, some might end up staying in hotel rooms until their travel documents can be prepared. ICE’s goal is to deport the families as quickly as possible.

The officials said ICE agents were targeting at least 2,000 immigrants who have been ordered deported — some as a result of their failure to appear in court — but who remain in the country illegally. The operation is expected to take place in at least 10 major cities.