Seventh Circuit Says Citation Verification Is Not Just the Filer's Problem

The Seventh Circuit added an important wrinkle to the growing line of AI-citation cases. The filing lawyer still owns the duty to verify authorities and quotations. But the court also suggested that opposing counsel may face criticism for failing to identify serious citation defects and bring them to the court's attention.

That is the practical lesson from Dec v. Mullin, a March 30, 2026 immigration decision. The underlying appeal was not about AI. The warning came from the briefing.

Petitioner's counsel cited two nonexistent cases and included a false quotation in the standard-of-review section. At oral argument, counsel denied using AI. A later letter said she had presumably copied and pasted the language from another brief she could not locate and had failed to verify the citations.

The Seventh Circuit admonished counsel but stopped short of stronger sanctions. The court emphasized that the errors appeared unintentional, counsel was contrite, and the fabricated authorities were used to support an undisputed legal standard rather than a contested merits issue.

The more interesting point was about the other side

The court repeated the familiar rule that trained lawyers must verify the citations and quotations in their own filings. But it then added that opposing counsel's failure to catch the defects and bring them to the court's attention also gave it pause, even if to a lesser degree.

That is not the same thing as announcing a free-standing duty to audit every sentence in an adversary's brief. The panel did not create such a rule. Still, the signal is clear. When serious authority defects are discovered, courts may expect someone on the other side to raise the problem rather than let it slide.

Why this matters

Most sanctions coverage still focuses on the lawyer who filed the defective brief. That remains the main risk, and Dec does not change it.

What the case adds is a response-side lesson. Citation verification is not just a filing control. It is also part of litigation hygiene once the defect is visible.

If opposing counsel discovers a nonexistent case, a quotation that does not appear in the source, or a proposition that does not match the cited authority, waiting until oral argument or final disposition may not be the safest choice. The better course may be to raise it promptly through a procedurally appropriate channel.

That framing fits the broader case pattern. In United States v. Farris, the Sixth Circuit focused on the filing lawyer's failure to verify quotations and case descriptions generated through Westlaw CoCounsel. In Lnu v. Blanche, the Ninth Circuit treated candor after discovery of the error as a major part of the discipline analysis. Dec does not conflict with those cases. It rounds them out.

A better litigation response pattern

Law firms do not need a broad new doctrine to act on this. They need a cleaner escalation rule.

When an adversary filing appears to contain fabricated or materially inaccurate authority, teams should:

• verify the cited source directly before making the accusation;
• preserve the defective language and the source comparison;
• decide quickly whether the issue should be raised through a letter, motion, meet-and-confer process, or the next scheduled hearing;
• avoid overclaiming if the problem is sloppiness rather than fabrication; and
• treat the issue as a filing-integrity problem, not a chance for rhetorical theater.

Bottom line

Dec v. Mullin does not create a formal duty to re-edit the other side's brief. It does something more practical. It suggests that when serious authority defects are discovered, courts may expect somebody on the other side to say so.

The filing lawyer still has the primary burden. But the safest appellate posture now looks broader than that: verify your own filing, and if the other side's filing contains serious authority defects, do not assume the court will be impressed if nobody raises them.

This article summarizes a published appellate decision and related litigation-risk implications. It does not provide legal advice.