Joinder's Diversity Asymmetry

Plaintiffs in federal diversity cases are barred from joining non-diverse supplemental parties or claims under 28 U.S.C. § 1367(b), but defendants can expand the case without the same restriction. This asymmetry codified the Supreme Court’s concern in Owen Equip. &amp; Erection Co. v. Kroger, that plaintiffs might so prefer federal court that they would “sneak” non-diverse parties into federal court by hiding them until after diversity jurisdiction is established, only then springing them on unsuspecting courts and defendants. This Article challenges the justification for the asymmetry in three ways.<br><br>First, it explores the history of the asymmetry, starting with how joinder rules developed as cases went from simple unilateral actions to the multi-party ecosystems of today, before examining the history of diversity and the supplemental jurisdiction statute. Second, it considers the theoretical bases for assumptions about jurisdictional preferences and how litigants achieve them, finding that the theory underlying the Court’s concern in Kroger is irrational and outdated. Third, the Article shares the results of an original empirical study of over 1,400 federal cases in which dispositive motions based on joinder and diversity jurisdiction were analyzed. The data show a pervasive inconsistency in the ways courts have attempted to address the asymmetry, even 35 years after the statute’s enactment, creating uncertainty for litigants and inefficiency for courts.<br><br>Taken together, the history, theory, and data show that the current rule produces structural inequality and procedural inefficiency. The asymmetry is an anachronism undercut by modern litigation tactics and disparate court resolutions. This Article concludes with a modest proposed revision to the statute that would eliminate the asymmetry in § 1367(b) while preserving diversity jurisdiction as a whole.