The regulation seeks to replace the so-called Flores Settlement Agreement, which requires that migrant children not be held in federal custody longer than 20 days. ABC was first to report on the new regulation.

A separate administration official says the basic idea is "to restore integrity through the process" because families could exploit the loophole, with the understanding that if they make it to the US as a family unit they'll be released soon.

The official says that there will be provisions under the rule for parole and bonding out that are "very lenient." The families who are not released will be held at family residential centers run by Immigration and Customs Enforcement throughout the parent's immigration proceedings.

More details about the proposed regulation are expected from the administration as soon as Wednesday.