Tiekert v. Village of Mamaroneck
U.S. District Court, Southern District of New York · S.D.N.Y. · New York bar guidance
Conduct
Counsel filed two oppositions with ChatGPT-supplied quotations and case characterizations he had checked only for existence and jurisdiction, then left the flagged errors uncorrected for months.
Consequence
Here the court found Rule 11 bad faith and imposed a $500 fine, two AI ethics CLE credits, a GenAI certification for future filings in the court, and service on the client.
Lesson
Here, confirming that a cited case exists and fits the subject matter was treated as no inquiry at all into whether the quotation or holding was accurate.
Verified September 29, 2026
- Citation
- Tiekert v. Village of Mamaroneck, No. 23-CV-8714 (CS), Order (S.D.N.Y. Sept. 14, 2026) (Seibel, J.), ECF No. 100
- Decided
- September 14, 2026
Summary
Plaintiff's counsel Brian M. Higbie filed oppositions to two motions to dismiss filed by two of the three individual defendants named in the Third Amended Complaint. Defendants' January 2026 replies flagged quotations that did not exist and misstated holdings. Higbie did not address the problem before the July 29, 2026 bench ruling, at which Judge Cathy Seibel walked through the defective authorities, including quotations she could not locate in Back v. Hastings on Hudson, Dorsett v. County of Nassau, Dillon v. Morano and Ragbir v. Homan, and characterizations of Mangino and Gonzalez v. City of Schenectady that the decisions did not support. She denied Murphy's request for Rule 41(b) dismissal and ordered Higbie to show cause under Rule 11(c)(3). In his response Higbie acknowledged relying on ChatGPT, said he had confirmed each case existed and was in the right jurisdiction but "did not independently verify the accuracy of the quotations or the characterizations of the holdings," and said he had returned to the tool after being told "that ChatGPT fixed the fabrication problem," despite an earlier hallucination in another matter. He admitted the Rule 11 violation and apologized.
- AI tool:
- ChatGPT (counsel acknowledged relying on it to research and draft the oppositions)
- Sanction amount:
- $500 payable to the Clerk of Court; two New York CLE credits in Ethics and Professionalism on AI by December 31, 2026; a GenAI-use certification on any future filing in the court researched or drafted with GenAI; service of the order on the client
What sanction did the court impose?
The court found a Rule 11(b)(2) violation, describing Higbie's verification as "wholly deficient to the point of being non-existent," and made the bad-faith finding the Second Circuit requires for sua sponte sanctions. It relied on conscious avoidance (he knew from prior experience that the tool could fabricate authority) and on his months of inaction after defendants flagged the errors. In setting the sanction it weighed that his conduct was not as brazen as some, his health and finances, that he did not appear to have other pending matters in the district, and that he "did not present wholly fabricated cases." It ordered him to pay $500 to the Clerk of Court within 30 days, complete two New York CLE credits on AI and its ethical use by December 31, 2026, attach a certification describing any GenAI assistance and how he verified its output to any future filing in the court for which he used GenAI (failure to include it "may result in additional sanctions"), and serve the order on his client. The court denied defense counsel's requests for $6,500 and $3,500 in fees because neither defendant had filed a Rule 11 motion, and Rule 11(c)(4) allows fee awards only when sanctions are imposed on motion.
Why does Tiekert v. Village of Mamaroneck matter for law firms using AI?
Tiekert is a sanctions order about fabricated quotations and misstated holdings in real cases, not invented case names. Judge Seibel located the violation in what counsel’s review skipped. Higbie had confirmed that each case ChatGPT supplied existed, sat in the right jurisdiction and dealt with the relevant subject, but had not read the passages he quoted. The court held that this “was no way an inquiry into whether his legal arguments were ‘warranted by existing law […]’” and that his “‘verification’ therefore in effect amounted to no inquiry at all.”
The bad-faith analysis turned on what counsel already knew. Higbie told the court he had seen ChatGPT supply a hallucinated case and an irrelevant one in an earlier matter, stopped using it, and then went back after “an acquaintance in the AI industry told him ‘that ChatGPT fixed the fabrication problem.’” The court described this as putting “blind trust in the bald assertions of an interested person without safeguards and in an effort to cut corners,” and found “conscious avoidance of the potential errors that he was introducing into his papers by relying on a tool he knew to be fallible.” His months of inaction after defendants’ replies flagged the quotations added to the finding.
The remedy was calibrated rather than severe. The court weighed that his conduct was not as brazen as that of some other attorneys, the absence of wholly fabricated cases, his health and finances, and that he did not appear to have other pending matters in the district, and settled on a $500 fine, targeted CLE, a forward-looking GenAI certification for his filings in the court, and service of the order on his client. It also enforced the procedural limit on fee awards: because the sanction was initiated by the court, Rule 11(c)(4) did not allow the defendants’ requested fees. Firms documenting compliance may wish to consider that, on this record, citation-existence checks alone did not satisfy the court’s view of Rule 11’s reasonable-inquiry requirement.
Implications for your firm
Operational steps a firm reading this case may wish to consider documenting. Strategic and rule-application calls belong to your firm's attorneys.
- Verify every quotation and characterization of a holding against the full opinion, not just the existence and court of the case. Here the court found counsel's existence-only check amounted to no inquiry.
- Review opponents' citation challenges item by item when they are raised. The court treated counsel's decision to check one flagged citation and dismiss the rest as contributing to its bad-faith finding.
- Document the firm's AI verification practice independently of vendor or acquaintance claims about tool accuracy; counsel's reliance on an acquaintance's assurance that the fabrication problem was fixed weighed against him.
- Consider that a sua sponte Rule 11 sanction in this circuit is payable to the court; here the defendants' fee requests were denied because neither filed a Rule 11 motion.