Most appellate briefs are snapshots in time. You file, the briefing closes, and the law keeps moving without you. Then a new decision lands that cuts directly to your issue. That is when the humble supplemental authority letter becomes one of the most consequential pages in your appeal.
Every jurisdiction handles these letters a bit differently. Federal Rule of Appellate Procedure 28(j) gives you 350 words. Some state courts allow a page or two. Others demand a bare citation and a pinpoint with no commentary, which can be both freeing and maddening. Regardless of format, the strategic judgment is the same: decide quickly whether the authority warrants a submission, craft a short explanation that advances your theme without rearguing, and file in a way that helps the court and avoids irritating it. A good appeals lawyer treats these letters like a scalpel, not a megaphone.
The purpose is not to re-brief
I once watched a panel stop counsel mid-argument and ask, “Why didn’t you file a letter when Jones came out?” Counsel responded that they’d covered the point in the reply. One judge looked down the bench and said, “But Jones changed the premise.” That exchange captures the point. Supplemental authorities exist to alert the court to recent developments that bear on an issue already briefed. They are not vehicles to sneak in new arguments or to reframe your case after the reply.
In practice, appellate lawyers tend to file three kinds of letters:
- A true update: a new case or statute after briefing that supports your position, undermines your opponent, or clarifies a standard. It was not available when you briefed. A necessary correction: an authority you overlooked that the panel or staff attorney will find on their own. You would rather own the mistake and provide the correct framing than let the other side define it. A fairness response: a short reply to your opponent’s letter when they push the boundaries, mischaracterize the new authority, or omit a limiting footnote that matters.
Most courts accept the first, tolerate the second, and strictly police the third. The better your judgment on whether to file, the more credibility you build for when it truly counts.
Timing is a form of advocacy
Speed matters more than length. When a major decision drops, clerks discuss it the same day. If it affects your appeal, the right time to draft is now, not next week. Several circuits expect a 28(j) letter within a few days of issuance. State appellate rules vary, but the practice norms are similar. An appeals attorney who waits until the eve of argument to “ambush” the panel with a complicated case will be remembered for the wrong reasons.
Speed, however, is not an excuse for sloppiness. A rushed, error-laden letter gets ignored or, worse, undercuts your reliability. Here is a practical rhythm that works in busy appellate litigation:
- Identify early: each morning, scan the relevant slip opinions and high court dockets. Many appellate attorneys use alerts keyed to citation strings and issue tags, not just case names. Evaluate in pairs: a senior and a junior lawyer spend 30 minutes deciding if the case truly intersects your issues. If yes, the junior drafts while the senior sketches the two-sentence takeaway. File cleanly: circulate internally for one round of line edits. Confirm the rule limits, finalize the citations and pin cites, and file that day if possible.
That cadence balances speed with accuracy, and it keeps the shop disciplined about not over-filing.
What counts as “pertinent”
Pertinence is narrower than relevance. The new authority must “pertain to” an argument you already made or an issue the court must decide. A new case on a neighboring doctrine rarely qualifies. Nor does an article, a practice guide, or a blog post, unless the local rule permits secondary sources, which is uncommon.
Examples help:
- You briefed a Chevron deference question. After briefing closes, the Supreme Court limits or clarifies agency deference. The decision is almost certainly pertinent. Your appeal turns on the harmless-error standard for admitting certain statements. A sister circuit issues a thorough harmless-error decision on nearly identical facts. It is likely pertinent, especially if your circuit often looks to that court. Your opponent cites a 1998 case for a broad rule. A new en banc decision curtails that rule. Even if the new case is not squarely on your facts, alerting the court is warranted. A district court order or unpublished state trial ruling that aligns with your theme is generally not pertinent, and many courts would strike or ignore it.
Experienced appellate lawyers also think about the panel. If a judge known for a particular doctrinal interest sits on your case, a new authority in that lane carries more weight.
The 350-word art form
FRAP 28(j) gives you 350 words, including everything but the case caption. Some state courts offer similar limits, and some require even less. The constraint is a gift. It forces the appeals lawyer to express a complex idea in a sentence or two, which is how judges share insights among themselves.
What belongs in a good letter:
- An opening line that orients the court: the new case name, court, date, and why it matters in one clean sentence. For example: “Yesterday, the Supreme Court decided Smith v. United States, which clarifies the materiality standard this Court must apply to appellant’s claim on Issue Two.” A surgical citation with pinpoint pages or paragraphs. If there is a crucial footnote, say so and cite it. A single sentence tying the new authority to your brief. Use the exact page numbers from your own brief where the issue appears. That tells chambers staff exactly where to cross-reference. One to two sentences addressing any tension or limitation. If the new case helps but has narrow reasoning, say so candidly. That honesty bakes in trust.
What never belongs: new facts, new issues, or argumentative flourishes. You are not “urging” the court to do anything. You are assisting the court by supplying a development in the law that fits the frame you already gave them.
Adding value without argument
Panels want context, not spin. Think of your letter as a navigation aid. Your job is to reduce the time between “What is this case?” and “How does it affect this appeal?” A helpful format often reads like good annotation:
Smith clarifies the materiality test in securities prosecutions by adopting the “reasonable investor under the circumstances” standard, rejecting the “market price impact” proxy used by Jones. See Smith, slip op. at 12-14. Appellant argued at Opening Br. 25-28 that the district court applied Jones’s proxy. Under Smith, the district court’s instruction, which equated materiality with any statistically significant price movement, was erroneous. See ER-412.
That is two sentences, not a new argument. You identified the standard, the component it displaces, the pages that matter, the pages in your brief addressing the issue, and the record cite where the problem resides. The appeals attorney who writes this way lets the panel use the letter immediately.
When the other side files first
Opposition letters often overreach. Appellate lawyers are tempted to respond point by point, which turns a crisp notification process into a shadow briefing cycle. Most courts disfavor that. Ask whether the opponent’s letter contains a concrete misstatement of the new case or a consequential omission. If yes, a short response that quotes the precise passage and supplies a pinpoint can be valuable. If not, resist the urge. The panel can read.
There are times, though, when silence hurts. In a trade-secret appeal, the other side submitted a new state supreme court decision construing “misappropriation” broadly. They left out a paragraph explaining that the opinion rests on a statutory clause not present in our jurisdiction. We filed a 200-word response with the parallel citation and the missing paragraph. Back at argument, one judge said, “That was helpful.” You do not get many on-the-record validations like that, but when they come, they follow restraint as much as clever drafting.
Anticipating questions at oral argument
A good supplemental letter is also a forecast. If a noteworthy case lands before your argument, expect the first question to come from it. The panel might ask whether the decision changes your standard of review, renders an issue moot, or affects remedy. The appeals attorney who wrote the letter has already mapped a crisp answer.
Prepare three pieces:
- A one-sentence rule statement you can deliver cleanly. If you cannot say it in one breath, rewrite it. A specific application to your record. Name the page, the witness, the exhibit. Judges appreciate concrete anchors. A short “even if” path if the case cuts against you. For example, “Even if Smith applies, the government cannot show materiality because the only price movement occurred three days later after unrelated news.”
You do not need to recite the letter at the podium. You need to show that you saw the same implications the court saw and that you have lived with them long enough to answer toward a practical disposition.
Risk management: when not to file
The worst letters telegraph insecurity. They string-cite marginal cases, announce articles, or parade unpublished orders that only clutter the record. Over-filing creates noise and dilutes attention to the one authority that deserved a spotlight.
Reasons to hold back:
- The new case shares vocabulary with your issue but turns on a distinct statute or regulatory scheme. The court will notice the mismatch and question your judgment. The authority is unpublished and your court disfavors or forbids citing it. Even where allowed, unpublished dispositions rarely carry weight unless the panel is already familiar with them. The case is in flux, for instance a grant of rehearing en banc or a stay that suspends precedential effect. Filing before the dust settles may leave you walking back your letter a week later.
You also weigh opponent incentives. If the case helps them more than you, silence may be strategic, especially if your panel seems set on a narrow ground. An experienced appellate attorney knows that restraint is often the better story to tell in chambers.
Technical compliance and filing hygiene
The administrative details are mundane until they cost you. Chambers remember the appellate lawyer who filed a noncompliant letter on appellate litigation the morning of argument. Avoid that footnote in their memory.
- Verify the rule and any local variations: word caps, attachments, whether you must provide copies, and timing relative to argument. Some state courts require leave of court. Use pinpoint citations, including paragraph numbers where applicable. If the opinion is not yet in a reporter, use slip opinion page numbers and provide a stable URL when permitted. Include an explicit cross-reference to your brief by page or section number. Do the reader the courtesy of a direct path. Keep the certificate simple and correct. Affirm compliance with the word limit. Do not attach the case unless the rule requires it. File early in the day. Clerks circulate letters internally; late filings sometimes miss the daily distribution and effectively lose a day of consideration.
These are small moves, but they add up to one impression: this appeals lawyer makes our work easier.
State courts and other variations
State appellate courts run the gamut. California allows post-briefing submissions but is sparing about argument in them. New York’s Appellate Division has different practices across departments. Texas often expects a motion for leave accompanied by the authority. You learn the local habits by reading orders in your venue and by asking colleagues who appear there frequently.
Criminal appeals sometimes involve a parallel stream of relevant developments, such as guideline amendments, retroactivity rulings, or changes to evidentiary standards. Those can be highly pertinent and also time sensitive. A federal appellate attorney who tracks Sentencing Commission updates knows when a vote turns from proposal to promulgation and whether that matters before mandate.
Administrative appeals present another wrinkle. An agency might issue new guidance mid-appeal. Whether that guidance qualifies as authority depends on your standard of review and the deference regime in play. If your theory attacks an interpretive rule as unreasoned, a new guidance memo may matter far less than a circuit decision construing the same statute. Spell that difference out succinctly if you submit anything at all.
Telling the court what to do, without saying so
Good supplemental letters respect the line between informing and arguing. Yet a seasoned appellate lawyer still guides the panel toward a useful disposition. That shows up in the selection of quoted text and in the choice of pin cites. You can highlight a remedial pathway without overtly urging it.
Example: a new case sets out a two-part harmless-error approach for a specific jury instruction mistake. Your letter quotes the sentence that defines the test and cites the page where the court remands for a limited new trial rather than a full retrial. You do not say, “Remand for a limited trial.” You let the authority show the panel an available route that fits your record.
This kind of curation is not coyness. It is respect for how judges read under time pressure. They lean on trusted advocates to flag where to look.
Coordinating inside a team
In larger appeals, multiple lawyers touch the brief. The risk of diffusion is real. Someone must own supplemental authorities from start to finish. That person’s name should be on the calendar for key court decision days. They should also coordinate with the client. Some clients will want to review every filing; others will trust your judgment to file within hours. Be clear about that expectation early.
Over the years, I have found it useful to keep a “shadow note” for each appeal, a living paragraph in the case memo that tracks potential developments, related en banc cases, pending cert petitions, and issue-hopping cases in adjacent fields. When a decision drops, you do not start research from scratch. You have already articulated the hinge points and the likely consequences. That prework turns a frantic 3 p.m. scramble into a measured 30-minute sprint.
Handling adverse authority honestly
Sometimes the new case hurts. Your instinct might be to let it lie and hope the panel does not see it. That instinct is rarely wise. Clerks will find it, and if your opponent files it first with a gloss that hardens against you, you are on your back foot.
Filing an adverse letter requires tone control. Acknowledge the holding. Identify the fact or statutory distinction that matters most. If a split exists, say so, but do not convert your letter into a survey. If the new case triggers an alternative argument you preserved, mention where that appears in your brief. You are equipping the court to reach your fallback cleanly if the primary path is blocked.
A real example: in a governmental immunity appeal, a new circuit decision narrowed the “clearly established” prong. We submitted a short letter with two sentences: one stating the new standard with a precise quote, the next pointing to our alternative argument about the absence of a constitutional violation at Opening Br. 31-36. At argument, the panel spent more time on the alternative, not because we argued hard in the letter, but because we pointed cleanly to the existing brief.
The ethics undercurrent
Supplemental authorities are not gamesmanship. Model Rule 3.3 requires candor to the tribunal. That duty often extends to controlling adverse authority in your jurisdiction, even if opposing counsel misses it. The borders vary by state and by court rule, but the spirit is constant: help the court get the law right.
Ethics also touch the mechanics. Do not bury a material limitation in a vague parenthetical. Do not omit a qualifying footnote that the panel would consider central if it surfaced another way. The short format cannot carry every nuance, but it must carry the material ones. The best appellate lawyers earn long-term credibility by writing letters that a judge can trust without fear of being misled by omission.
When supplemental authority shifts the remedy
The most consequential letters sometimes do not change who wins, but they change what happens next. A new case may redefine prejudicial error, adjust the standard for remand instructions, or refine mootness exceptions. That shifts the remedial posture.
Be explicit about the intersection. If a decision endorses limited remands to address a discrete question, identify the question your record cannot answer under the new rule. Panels do not love remands born of vagueness. They will, however, send the case back with tight guidance if you furnish a principled boundary. One sentence can do a lot of work: “Under Smith’s two-step inquiry, the district court made no finding on X, which this Court cannot resolve on this record.” That is not overarguing; it is clearing the path.
After the letter: update your strategy memo
Once filed, the letter is only part of your job. Update your client and your internal strategy memo. If oral argument is upcoming, adjust your outline headings so that the new authority sits where a question is most likely to arise. If the opinion issues post-argument but pre-decision, consider a short follow-up only if it directly answers a question the panel asked. Otherwise, let the argument speak.
When judgment enters and the mandate later issues, keep the file note that tracked your supplemental authorities. It becomes a resource on future cases and a teaching tool for newer appellate lawyers in your shop.
A few lines on tone and voice
Appellate practice rewards light touch and precise language. The same holds for supplemental authorities. Avoid “We submit” and “We respectfully urge” in these letters. Let the facts, the record, and the citation do the talking. Use ordinary words. Write short sentences when the point is delicate. Cut legalese that bloats 26 words where 11 will do. If your sentence sounds like it is auditioning for a law review, rewrite it for the human who will read it at 7:15 a.m. with coffee and three other files open.
Why the small page matters
For an appellate attorney, credibility is the coin of the realm. You earn it one page at a time. A sharply crafted supplemental authority letter tells a panel several things about you: you watch the law closely, you move promptly, you know the difference between argument and assistance, and you can distill a complex development into something the court can use immediately. Over the span of a career, that reputation pays off in how chambers read your briefs, how they frame questions at argument, and how they describe your advocacy to colleagues.
Plenty of appeals are won or lost on the briefs, and many never need a supplemental letter. When one does, treat it like a small, decisive brief. The discipline you bring to those 350 words reflects your entire approach to appellate litigation, and judges can tell.