I found this statement in Justice Alito’s dissent in the Fair Housing case to be curious:

The Court also stresses that “many of our Nation’s largest cities—entities that are potential defendants in disparate-impact suits—have submitted an amicus brief in this case supporting disparate-impact liability under the FHA.” Ante, at 23–24.

This nod to federalism is puzzling. Only a minority of the States and only a small fraction of the Nation’s municipalities have urged us to hold that the FHA allows disparate-impact suits. And even if a majority supported the Court’s position, that would not be a relevant consideration for a court. In any event, nothing prevents States and local government from enacting their own fair housing laws, including laws creating disparate-impact liability. See 42 U. S. C. §3615 (recognizing local authority).

Although Justice Alito says these shouldn’t count, he’s also saying that if you do this, you want to get a lot of states and municipalities on board.