Yet another appeals court has rejected the idea that so-called parens patriae lawsuits—in which a state government sues on behalf of its citizens—are just class actions in disguise.

In a 19-page decision issued on Jan. 9, the U.S. Court of Appeals for the Second Circuit refused to hear an appeal by Purdue Pharma in a case that the Kentucky attorney general brought against Purdue Pharma over its marketing of the painkiller Oxycontin.