Stephen Miller wants to separate families at the border again.

The White House is considering a new approach to deter families seeking to enter the country illegally at the southern border, using a system called “binary choice,” in which, according to the Washington Post, families who claimed asylum would be detained as a unit for “up to 20 days” and then parents would get the choice: “stay in family detention with their child for months or years as their immigration case proceeds, or allow children to be taken to a government shelter so other relatives or guardians can seek custody.”

The impetus for this, the Post reports, is frustration with an increase in unauthorized border crossings by migrant families, which had risen almost 40 percent in August to a “record level” and was expected to rise further in September.

White House adviser Stephen Miller, according to the Post, is the driving force behind the planning, because he viewed the much-critcized child separations in May and June as “an effective deterrent to illegal crossings.”

Any new policy that seeks to either separate parents from children or keep children in detention for more than 20 days would likely run into legal trouble because of a 1997 federal court settlement, expanded in 2015, that limits the government to detaining child migrants for no more than 20 days. The Post reports that federal officials are thinking of ways to get out from under the agreement to allow for longer periods of detention for asylum-seeking families with children.

Any large scale new detention policy would also require more infrastructure for housing—the Post reports that Immigration and Customs Enforcement has only three centers designed for families of migrants. In total, they can accommodate 3,000 people, about a quarter of the total crossings per month.