The Trump administration announced a new rule on Wednesday that would allow migrant families who crossed the border illegally to be kept in detention centers long-term.Why it matters: A decades-old court decision — the Flores agreement — has prevented the government from holding minors in detention for longer than 20 days. The new regulation would replace that and give the federal government more power in determining how to care for migrant minors and families in its custody. The rule was first proposed following the family separation crisis last year, and is certain to face legal challenges. Any court case would end up before California federal Judge Dolly Gee — the same judge who oversaw the Flores case and refused to grant Trump's earlier request to change the decision to allow families to be detained together long-term. The big picture: The new rule would also allow DHS to license and inspect its own facilities and authorize the department to set the standard of care required for migrant children, America's Voice DHS Watch director Ur Jaddou told Axios. Context: A 2001 Supreme Court ruling already ensures that no migrants are detained longer than 180 days except for special circumstances. This would still apply for migrant families. The Flores agreement was a 1997 court settlement that dictates how the federal government must care for migrant minors in its custody.The 20-day detention limit originally only applied to migrant kids who crossed the border illegally without their parents. But in 2015, Judge Gee ruled that the 20-day limit also applied to minors who are with their parents.Between the lines: Long court backlogs make it next to impossible for a family immigration case to be completed within 20 days, forcing the government to release migrant families until their court dates — or separate kids from their parents, which the Trump administration did last year.