When a warning letter arrives from a patent holder: what to do first
Read the letter in full before doing anything else, then stop replying informally. The first step is to identify the exact right claimed, preserve the product or process named in the letter, and assign one person to own the file. Any period the letter sets for a reply starts running from the date of receipt, not from the date a response is drafted. What happens next depends on whether the patent is a national patent or a European patent with unitary effect.
Legal basis for the response
The framework that applies depends on the type of patent named in the letter. If it names a European patent with unitary effect, the forum and procedure are set out in the Agreement on a Unified Patent Court, read together with Regulation (EU) No 1257/2012 and Council Regulation (EU) No 1260/2012, which govern the translation arrangements for the same patent. All three instruments entered into force on 1 June 2023.
If the letter instead names a national patent, or a European patent for which unitary effect was never registered, the Agreement on a Unified Patent Court does not apply. The matter then proceeds under the patent law of the country where the patent is registered, and that law sets its own deadlines and its own competent court.
What changes once the letter is received
Receipt of the letter carries legal weight on its own, regardless of whether the underlying claim turns out to be sound. Any period the letter names for a reply, an undertaking, or the withdrawal of a product begins to run from the date of receipt. Leaving the letter unanswered does not pause that period, and it does not stop the sender from proceeding directly to a court once the period has passed.
A written reply that is inaccurate, incomplete, or admits more than intended is hard to withdraw once it exists. That reply, not the letter itself, is where most of the practical risk sits in the first days after receipt.
What to do, in order
- Record the date of receipt and appoint one internal owner for the file.
- Stop informal replies by email, phone, or messaging from anyone other than that owner.
- Preserve the product, code, drawings, or samples named in the letter exactly as they stand.
- Check whether the patent named in the letter is in force and covers the jurisdiction where the business operates.
- Confirm that the sender is the patent holder, or holds a mandate to act for the patent holder.
- Route the file to counsel before any period stated in the letter lapses.
Who decides, and where
Where a dispute ends up if the letter is not resolved depends on the type of patent asserted. The table sets out the three main configurations.
| Type of patent named in the letter | Governing instrument | Competent forum |
|---|---|---|
| European patent with unitary effect | Agreement on a Unified Patent Court; Regulation (EU) No 1257/2012 | Unified Patent Court |
| Classic European patent, opted out of unitary jurisdiction | national patent law of the country of registration | national court |
| National patent | national patent law of the country of registration | national court |
The same table governs which body decides on interim measures, such as a request to stop distribution before a full hearing. That decision follows the same forum as the underlying dispute.
If your situation differs
- If the letter names a European patent with unitary effect and no opt-out was filed, the dispute belongs before the Unified Patent Court, and any reply should be drafted with that forum in view from the outset.
- If the letter names only a national patent, the reply follows the civil procedure of that country, and the Agreement on a Unified Patent Court has no bearing on it at all.
- If the real dispute is less about patent validity and more about who owns the underlying result, the same first-response logic applies elsewhere too: When an agency keeps the design files and its owner is contested follows a comparable order of steps.
- If the asset in question is a token rather than a patent, a parallel sequencing question is answered on its own page: What to do first in this situation step by-step guidance there mirrors the order set out above.
What this page does not cover
This page does not assess whether the patent named in the letter is valid, novel, or actually infringed. It does not set the value of any settlement, and it does not replace the procedural deadlines of whichever jurisdiction or forum turns out to apply once the file is reviewed. It also does not cover a separate question that sometimes accompanies a warning letter: whether the sender's own handling of personal data rests on a legitimate interest. Legitimate interest assessment: summary explained sets out that test on its own page.
Confirming who genuinely stands behind the letter, rather than judging the letter's legal merits, is a factual question, and it can often be answered before any reply is sent: Counterparty in Estonia step by step shows what a registry-based check establishes.
Related situations
A related situation, where customs action rather than a letter triggers the first response, is covered separately, including the role customs enforcement plays under Regulation (EU) No 608/2013: When a customs authority detains a shipment explained sets out that sequence.
Sources and verification
This page was checked against the sources below on 4 March 2025. Where the letter names a patent type not covered here, the check should be repeated against the register entry for that specific patent.
- Agreement on a Unified Patent Court
- Regulation (EU) No 1257/2012
- Council Regulation (EU) No 1260/2012
Frequently asked questions
What is the first step when a warning letter arrives from a patent holder?
Record the date of receipt, preserve the product or files named in the letter, and assign a single owner for the file before anyone replies. Do not admit or deny infringement in an informal message.
Which deadline is already running?
Any period the letter states for a reply, an undertaking, or a withdrawal of the product begins on the date of receipt, not on the date a response is prepared. The letter itself, not a later confirmation, sets the starting point.
Who decides, and on what evidence?
The competent forum depends on the type of patent named. A European patent with unitary effect falls under the Agreement on a Unified Patent Court and is decided by the Unified Patent Court; a national patent, or an opted-out European patent, is decided by the national court of the country of registration, on the evidence each party submits there.