Protective letter: what the decision maker looks at
A protective letter tells the court or patent office why an interim injunction against you would be premature. The decision maker checks whether the filing is complete, whether the timing is plausible, and whether the letter answers the specific claim the other side is likely to raise. Miss any of the three and the letter reads as noise, not as a defence.
What the decision maker checks first
Completeness comes first. A protective letter with gaps in the chain of rights, or without a clear description of the product at risk, gets set aside before the substance is read. Plausible timing comes second: the letter has to acknowledge that a request for an injunction could arrive within days, not months, and explain why the filer is not the one who should move first. The third test is the sharpest. The decision maker reads the letter against the claim it expects, not the claim you fear. If the letter answers a different dispute, it does not help you when the real request lands. Letters written in general terms, covering every possible claim at once, tend to fail this test. A letter that names the likely opponent, the likely product, and the likely legal theory performs better, even when it runs shorter.
A common failure is treating the letter as a summary of the invention rather than as an answer to a possible claim. The two documents look similar on the page, but the test applied to them is not the same, and a letter written like a technical brief tends to stall at the completeness check before it reaches the substance.
Stages and typical timing
The letter moves through four stages once it is filed. None of the stages has a fixed statutory length; each office and court sets its own internal pace, and pace shifts with caseload.
| Stage | What happens | Typical pace |
|---|---|---|
| Filing | Letter and supporting documents lodged with the registry or court file | Same day the file is opened |
| Screening | Registry checks the filing is complete and properly served | A few working days |
| Substantive review | Decision maker reads the letter against any incoming request | Only triggered once a request for an injunction actually arrives |
| Expiry or renewal | Letter lapses after the period set by the forum, unless renewed | Renewal is the filer's responsibility, not the registry's |
Documents to prepare
Assemble the file before drafting starts. A late document usually forces a refiling, and a refiling resets the clock the letter was meant to beat.
- Evidence of the right at stake, including the chain of title where the right passed between parties.
- A description of the product or process the letter defends, precise enough to match a possible claim.
- A short account of prior contact with the other side, if any took place.
- Contact details for counsel authorised to receive service on short notice.
- A signed authorisation from the person or entity filing the letter.
Where the forum sits in a different jurisdiction from the filer, a certified translation of the core evidence should sit in the file alongside the original, ready before it is requested.
Who decides and where
The forum depends on where the anticipated claim would land, not on where the filer is based. In most patent disputes this is the same court or office that would hear the injunction request itself. There is no separate panel for protective letters; the same decision maker who would grant or refuse an injunction reads the letter first, if one has been filed.
The reviewing office does not hold a separate hearing to consider the letter; it keeps the letter on file and reads it once a matching request for an injunction is lodged. Where more than one forum could plausibly hear the claim, the practice is to file in each one separately. A letter filed in the wrong forum does not transfer.
The point of no return
Once a request for an injunction is served, the protective letter can no longer be filed for the first time; it can only be relied on if it was already in the file. Filing after service is treated as a response to the claim, not as a protective measure, and it loses the procedural advantage the letter is meant to secure.
Practitioners sometimes assume a late letter still counts as a defence; in practice, the decision maker treats it as a submission responding to the claim already served, which shifts the burden back onto the filer. The safe rule is to file before any contact with the other side moves past routine correspondence.
If your situation differs
If you have already received a warning letter from the rights holder, file the protective letter immediately; a warning is often the last signal before a request for an injunction follows.
If the dispute involves a token representing the right rather than the right itself, the chain of evidence the decision maker checks is different — Who decides and when in this situation and its walks through that chain in a neighbouring practice area.
What this page does not cover
This page does not cover how the letter is drafted clause by clause. It does not tell you whether your case is strong enough to justify the effort — that assessment depends on documents this page cannot see. It does not replace advice on the substance of the underlying right, and it does not predict how a specific decision maker will rule once the letter is read. It also does not cover cross-border service of the eventual injunction request, which follows its own timetable.
Verified
This page describes procedural practice across patent offices and courts and does not cite specific statutory provisions, in line with how procedural pages on this site are built. Sources by tier and delivery route overview and who explains how source tiers are assigned and checked across the site.
Where the underlying dispute touches a supplier chain rather than a single counterparty, the questions the decision maker asks about evidence overlap with due-diligence questions elsewhere — Counterparty report when a subprocessor is added in practice shows how that overlap is handled on the reporting side.
Related reading
Cross-border cases raise a parallel question about how the initial claim reaches you at all — Cross-border service of documents step by step sets out what the decision maker checks there.
FAQ
How long does a protective letter take in practice?
Filing itself takes a day once the documents are ready. The letter then sits in the file, unreviewed, until a request for an injunction arrives — that wait can run from weeks to years, or never happen at all.
Which documents are needed to start?
At minimum: proof of the right, a description of the product or process at risk, and a signed authorisation for whoever files. Everything else strengthens the letter but is not strictly required to open the file.
What happens if the other side does not respond?
Nothing happens on a fixed schedule. The letter has no deadline that forces the other side to react; it waits until they choose to file for an injunction, if they ever do, and the decision maker only reads it at that point.
If an assignment on the same file is still unsigned while work has already moved forward, close that gap before drafting any protective letter — When the assignment is unsigned but performed explained sets out what to fix first.