The Class Action Fairness Act (CAFA) extends federal diversity jurisdiction to certain “mass actions” involving “100 or more persons.” 28 U.S.C. § 1332(d)(11)(B)(i). One might think that since CAFA was passed in 2005, the notion of mass action would have been fully analyzed. The Supreme Court has long construed jurisdictional statutes like CAFA to establish “simple” bright-line rules. Hertz Corp. v. Friend, 559 U.S. 77, 94–95, 130 S.Ct. 1181, 175 L.Ed.2d 1029 (2010); see Sisson v. Ruby, 497 U.S. 358, 375, 110 S.Ct. 2892, 111 L.Ed.2d 292 (1990) (Scalia, J., concurring in judgment) (eschewing “the sort of vague boundary that is to be avoided in the area of subject-matter jurisdiction wherever possible”). Yet plaintiffs continue to bring mass actions in state courts. At issue in Adams v. 3M Co., 65 F.4th 802 (6th Cir. 2023) was whether two state-court complaints, each joining more than 100 plaintiffs, qualified as CAFA mass actions. Plaintiffs were miners who alleged they wore defendant’s respirators to protect their lungs from coal dust, but nevertheless developed pneumoconiosis, a disease caused by inhaled dust particles.

One complaint named more than 400 co-plaintiffs, demanded “judgment” against all defendants “jointly, severally, and/or individually,” and sought “a trial by jury on all issues so triable.” The second complaint named more than 300 co-plaintiffs and mirrored the first. Defendant removed the cases to federal court on CAFA, federal question, and diversity grounds. The district court, surprisingly, remanded them to state court. 3M sought leave to appeal, as under § 1453(c)(1), “a court of appeals may accept an appeal from an order of a district court granting or denying a motion to remand a class action.” For purposes of the section, “a mass action shall be deemed to be a class action.” 28 U.S.C. § 1332(d)(11)(A).

There was no dispute that lawsuits qualify as “civil action[s]” and seek “monetary relief.” That left one question: Had plaintiffs proposed to try claims of 100 or more persons … jointly on the ground that the claims “involve common questions of law or fact”? The 6th Circuit observed that the miners’ complaints did just that. Start with the first phrase. A litigant proposes to try claims “jointly” if he offers to try them through a common judicial process. Claims presented in a single complaint proceed through a common trial process absent an order to the contrary. When plaintiffs each filed complaints with more than 100 co-plaintiffs, they offered to try their co-plaintiffs’ claims jointly. See In re Abbott Lab’ys, Inc., 698 F.3d 568, 572 (7th Cir. 2012) (“[O]ne complaint implicitly proposes one trial ….”).

Turn to the second phrase. A litigant proposes a joint trial “on the ground[s] … [of] common questions of law or fact” when he offers, as a basis or reason for joint proceedings, the contention that the claims involve common questions. By filing a complaint predicated on a “common” “question of law or fact,” plaintiffs thus offered the presence of common questions as a “ground” for pursuing a joint trial, 28 U.S.C. § 1332(d)(11)(B)(i).

CAFA targets putative class actions and lawsuits that resemble them—“mass actions” in short. Mississippi ex rel. Hood v. AU Optronics Corp., 571 U.S. 161, 173–74, 134 S.Ct. 736, 187 L.Ed.2d 654 (2014). Lawsuits like the miners’ complaints fit the bill, said the court. They assert parallel claims on behalf of more than 100 plaintiffs, all proceeding on the theory that the claims are similar enough to merit adjudication in tandem. Every circuit to consider the question agrees. “Where a single complaint joins more than 100 separate claims involving common questions of law and fact, there is a presumption that those plaintiffs have implicitly proposed a joint trial.” Ramirez v. Vintage Pharms., LLC, 852 F.3d 324, 329 (3d Cir. 2017); see Lester v. Exxon Mobil Corp., 879 F.3d 582, 585–89 (5th Cir. 2018); Abbott Lab’ys, 698 F.3d at 572; Atwell v. Bos. Sci. Corp., 740 F.3d 1160, 1163–66 (8th Cir. 2013); Visendi v. Bank of Am., N.A., 733 F.3d 863, 869 (9th Cir. 2013); Scimone v. Carnival Corp., 720 F.3d 876, 881–82 (11th Cir. 2013); cf. Parson v. Johnson & Johnson, 749 F.3d 879, 888 & n.4 (10th Cir. 2014) (suggesting the same); accord 2 William B. Rubenstein, Newberg & Rubenstein on Class Actions § 6:25 (6th ed. 2022).

The miners respond that, under Kentucky or federal law, their cases may not ultimately involve common questions of law or fact. Still, an ultimately unwarranted proposal remains a proposal. See Visendi, 733 F.3d at 867–71. Nor did it matter that a joint trial may never result, perhaps even on a defendant’s motion to bifurcate or sever. Here, each filed a complaint joining more than 100 co-plaintiffs and seeking “a” jury trial. See Ramirez, 852 F.3d at 327 (requiring an “explicit and unambiguous disclaimer” of a joint trial).

In the alternative, plaintiffs asked the court to affirm the remand order under CAFA’s “local controversy” exception. See 28 U.S.C. § 1332(d)(4). But for the exception to apply, the miners needed to show that a Kentucky defendant’s conduct “forms a significant basis for the[ir] claims.” Mason v. Lockwood, Andrews & Newnam, P.C., 842 F.3d 383, 388, 395–97 (6th Cir. 2016). Here, the “core” of the miners’ complaints alleged that out-of-state defendants designed, manufactured, and sold defective respirators, and plaintiffs offered no reason for thinking that the defendant local merchants’ liability was anything but derivative of the manufacturer’s alleged liability. Remand reversed.