We’ve only discussed Shady Grove Orthopedic Associates, P.A. v. Allstate Insurance Co., 559 U.S. 393 (2010), a couple of times. Shady Grove, displaced – in federal court – a variety of state-law limitations on class actions because those restrictions were at odds with Fed. R. Civ. P. 23, and in federal court federal rules properly enacted under the Rules Enabling Act, 28 U.S.C. §2072 (“REA”), control. Thus, the plaintiffs in Shady Grove could bring state-law class actions in federal court that were barred in state court.
Earlier this week, in Berk v. Choy, 2026 WL 135974 (U.S. Jan. 20, 2026), a unanimous Supreme Court struck again, holding that a relatively common state-law restriction on medical malpractice claims – a requirement that the complaint be accompanied by an “affidavit of merit” signed by a doctor – did not apply in federal court because that requirement was beyond what was needed to satisfy Fed. R. Civ. P. 8.
The Court’s analysis in Berk seems equally relevant to the requirements of any federal rule. First, the “Rules of Decision Act [28 U.S.C. §1652] dictates that state substantive law must yield if . . . a [federal] statute “otherwise require[s] or provide[s].” Berk, 2026 WL 135974, at *3. Second, the REA is such a statute, since it “authorizes“ the Supreme Court to “prescribe general rules of practice and procedure and rules of evidence,” §2072(a), “for district courts, [and] provides for the application of federal law.” Berk, 2026 WL 135974, at *3 (citations omitted). Thus, “a valid Rule of Civil Procedure displaces contrary state law even if the state law would qualify as substantive under Erie’s test.” Id. (emphasis added). As will become clear, we think that’s important.
Think about that again. The Supreme Court just unanimously held that anything in state law, whether “procedural” or “substantive” goes out the door in federal diversity cases, to the extent that it “demands more,” 2026 WL 135974, at *4, than a federal rule – unless the rule itself exceeds the scope of the REA. Id.
The state affidavit-of-merit requirement demanded more than Rule 8, since that rule has no requirement to include “evidence” (the affidavit) in a complaint. Id. (“Under Rule 8, factual allegations are sufficient, but under the Delaware law, the plaintiff needs evidence too.”). “The two rules thus give different answers.” Id. Nitpicking – that the affidavit was “a separate sheet of paper” from the complaint itself – was unsuccessful. Id. What matters is whether the state requirement and the applicable federal rule “address[] the same issue – and in doing so, impose[] a different standard.” Id. (footnote omitted). A number of more case-specific arguments made by the malpractice defendants also failed. Id. at *5-6.
Those defendants’ final fallback position fared no better. No, Rule 8 did not violate the REA because it was improperly “substantive.” Id. at *6.
For purposes of the Rules Enabling Act, we use a modest test: whether the Federal Rule really regulates procedure. Or put differently, what matters is what the Rule itself regulates. . . . In applying this analysis, we have rejected every statutory challenge to a Federal Rule that has come before us.
Berk, 2026 WL 135974, at *6 (citations and quotation marks omitted). Berk had no trouble determining that Rule 8 – enacted as a Federal Rule of Civil Procedure – “really regulates procedure.” Id. While it had “practical effect on the parties’ rights,” it did not regulate “the rights themselves.” Id.
Nor was Berk willing to change the Court’s long-standing refusal to evaluate the nature of the state law being displaced:
[Defendants] argue that determining whether a Rule is valid under the Rules Enabling Act requires asking a second question: whether the displaced state law is substantive. We rejected that approach eight decades ago and decline to reconsider it now. On the contrary, we underscore that “the substantive nature of [a state] law, or its substantive purpose, makes no difference.
Berk, 2026 WL 135974, at *7 (citations omitted) (emphasis original).
So what can we take away from Berk? Start with medical malpractice, the subject of the state legislation overturned (preempted?) in Berk. Most p-side lawyers specializing in such cases wouldn’t be caught dead in federal court if they could help it. Does that change? Maybe some in the short term, but probably not in the long term. Most malpractice cases are non-diverse to start with, and the sorts of malpractice plaintiffs likely to have trouble satisfying certificate-of-merit requirements don’t have very good cases anyway, so we question how many will want to “make a federal case” of it.
On the other side, if the states have the political will to do so, it wouldn’t be hard to fix the federal rules problem that did in this particular certificate-of-merit statute. Just tie the requirement to something that the federal rules don’t reach. A certificate/affidavit mandate as part of initial discovery might run afoul of Fed. R. Civ. P. 26(a)(2) governing initial disclosures. So tie such mandates to something else. The statute of limitations for medical malpractice could be 180 days, unless the plaintiff submits a certificate of merit, in which case it’s the same length it was before. Or, because medical malpractice cases without certificates of merit are highly likely to be bogus, the damages cap for such cases is very low, whereas with the certificate, it is whatever state law now requires. Because an amended certificate/affidavit mandate no longer has anything to do with anything a federal rule covers, it should have no trouble with Berk.
What else? Well, here’s an interesting piece discussing how Berk might cause trouble for parties in federal court seeking dismissal of litigation under state “Anti-SLAPP” statutes. Nor should state restrictions on informal interviews with plaintiffs’ treating physicians apply in federal court in derogation of broader federal discovery rules.
But we hasten to point out that Berk implicates more than just the Federal Rules of Civil Procedure. As we quoted at the beginning of this post, the Federal Rules of Evidence also stem from the REA and apply in federal court under the Rules of Decision Act. That’s why Rule 702 is so important in federal prescription medical product liability litigation. But other state-law evidentiary peculiarities besides expert testimony could well conflict with the Federal Rules of Evidence – particularly the liberal admissibility requirements of Fed. R. Evid. 401 and 402. Rule 401 provides that “Evidence is relevant if . . . it has any tendency to make a fact more or less probable than it would be without the evidence.” Rule 402 provides that “[r]elevant evidence is admissible” subject to a number of exceptions that do not include any form of state law.
In a prior post from a couple of years ago, we discussed the original Shady Grove decision in the context of a couple of ways that Pennsylvania evidentiary restrictions in product liability cases could be trumped by the broader admissibility standards of Fed. R. Evid. 401-02. Berk only reinforces those arguments, with its repeated emphasis that, when federal rules are involved, whether the state law being displaced is “substantive” or “procedural” doesn’t matter a hill of beans. Subsequent Pennsylvania developments only increase the importance of applying the Federal Rules of Evidence in federal court. Since that post, the Pennsylvania Supreme Court has made Pennsylvania the only state in the nation where compliance with industry and governmental (in our sandbox read, FDA) standards is not even admissible in strict liability actions. See Sullivan v. Werner Co., 306 A.3d 846, 862-63 (Pa. 2023) (plurality opinion), affirming, 253 A.3d 730, 747 (Pa. Super. 2021) (discussed in detail here).
Under Berk and Fed. R. Evid. 401-02, that evidentiary restriction should not apply in federal court. And it hasn’t, even before Berk. The Third Circuit has repeatedly held that the Federal Rules of Evidence govern in diversity product liability cases otherwise subject to state law. E.g., Covell v. Bell Sports, Inc., 651 F.3d 35, 36-37 (3d Cir. 2011); Moyer v. United Dominion Industries, Inc., 473 F.3d 532, 546 (3d Cir. 2007); Diehl v. Blaw-Knox, 360 F.3d 426, 431 & n.3 (3d Cir. 2004); Rolick v. Collins Pine Co., 975 F.2d 1009, 1013 (3d Cir. 1992):
The issue to be decided here is whether the OSHA regulation is admissible in a diversity action as evidence of the standard of care owed by the defendants to the plaintiff. . . . Since the question involves the admission of evidence in a federal court, the Federal Rules of Evidence control. . . . We can think of no reason under the Federal Rules of Evidence why the OSHA regulation is not relevant evidence of the standard of care once it is determined, as we have done, that under Pennsylvania law the defendants could owe plaintiff a duty of care.
Rolick, 975 F.2d at 354. See Kelly v. Crown Equipment Co., 970 F.2d 1273, 1278 (3d Cir. 1992) (strict product liability case; federal rule admitting subsequent remedial measures “is ‘arguably procedural,’ and therefore governs in this diversity action notwithstanding Pennsylvania law to the contrary”). NOTE: none of these cases involve prescription medical products. That’s because Pennsylvania has strictly enforced Restatement (Second) of Torts §402A, comment k (1965), and not applied strict liability to prescription products.
Berk only reinforces this Third Circuit precedent, so in Pennsylvania federal court product liability litigation, compliance evidence should be admissible regardless of Sullivan. Thus, Third Circuit Rule 401-02 decisions in product liability cases applying Pennsylvania substantive law should apply, notwithstanding Sullivan. Federal standards on what‘s “relevant,“ rather than Pennsylvania’s exclusion of compliance evidence based on its peculiar (and probably “substantive”) reading of Restatement §402A. As to the admissibility of compliance, Pennsylvania law plainly “demands more” than Rules 401-02 and when applied to compliance evidence would “give different answers” to admissibility. Berk, 2026 WL 135974, at *4. Since it can hardly be denied that Rules 401-02 “really regulate” evidence, that Pennsylvania might consider its more restrictive approach “substantive” is of no consequence. Id. at *6.
To the extent that states have other restrictive evidentiary rules that disfavor defendants (statutes barring admission of seatbelt nonuse come to mind), a similar rationale should apply after Berk.