In May 2023, New York lawyer Stephen Schwartz submitted a federal-court brief in Mata v. Avianca, a personal-injury lawsuit against the airline, containing six fabricated case precedents produced by ChatGPT. The citations appeared plausible but referred to nonexistent decisions, opinions, and quotations. Schwartz said he had not previously used ChatGPT and did not understand that its output could be fabricated; he also reported that the system continued insisting the authorities were genuine when questioned.
The episode triggered sanctions and broader judicial warnings about generative AI in legal practice. Northern District of Texas Judge Brantley Starr required lawyers filing in his court to certify that AI-generated work had been checked by a human, citing hallucinated quotations and citations as well as bias and the absence of any professional duty to truth. By 2025, a database tracking AI hallucinations in legal proceedings had recorded more than 1,300 incidents, underscoring that the problem had moved beyond isolated experimentation into institutional court practice.