# The inventors could challenge. The Director could refuse. Assignor estoppel doesn’t bar an IPR: a 2013 Board decision, precedential as to § II.A only, and the Federal Circuit agree. In 2025 the Acting Director denied review anyway, where inventors who had assigned their rights were behind the petition. In 2026 the Federal Circuit declined to step in. Sources checked October 16, 2026 **Allowed, then refused** Tessell could file under the statute. The Acting Director still withdrew institution, and the court denied mandamus. ## Before you read Inventors who assigned a patent start a company, and it petitions for IPR. Can the Office refuse to hear it, even though assignor estoppel doesn’t apply? - No: the statute lets any non-owner file - Yes: it did in Tessell, on discretionary grounds - Only if a court has applied estoppel first Yes. In Tessell (Aug. 22, 2025), the Acting Director acknowledged assignor estoppel doesn’t apply in IPR, but vacated institution and denied the petition as an inefficient use of review. ## The founder’s company Robert Schad was a named inventor on a Husky Injection Molding patent. He was also the founder, co-owner, president and CEO of Athena Automation, and one of its two directors. When Athena petitioned to cancel the patent’s claims, Husky made one argument: an inventor’s company shouldn’t be allowed to attack the inventor’s own patent. The Board instituted review of all 22 challenged claims. Athena, § II.A ## Start with the statute Assignor estoppel is an equitable doctrine from the courts. Someone who assigns a patent, often an inventor assigning to an employer, generally can’t later argue in court that it is invalid. The Board began with the text instead: “a person who is not the owner of a patent may file with the Office a petition to institute an inter partes review.” An assignor, no longer the owner, is that person. Athena 35 U.S.C. § 311(a) The Board contrasted the International Trade Commission, where the statute provides that “[a]ll legal and equitable defenses may be presented in all cases.” “Congress issued no similar statutory mandate to the Office in connection with AIA post-grant reviews.” And “none of Husky’s arguments addresses the language of § 311(a).” Athena, pp. 11–13 The Federal Circuit later agreed. In Arista v. Cisco, it held that the statute’s language leaves no place for assignor estoppel in IPR. Arista, pp. 17–23 ## Eligible, and refused Tessell’s founders and employees included inventors who had assigned their rights to Nutanix. The Board instituted one of Tessell’s challenges; a related one had been denied. On August 22, 2025, the Acting Director vacated the institution and denied the petition. Tessell, pp. 2–3 The order expressly acknowledged that assignor estoppel does not apply. It found review inefficient where the inventors now argued the claims were unpatentable. Tessell’s argument about broader claims in later patents of the family also lacked a sufficient comparison with the originally filed specification. Tessell, pp. 2–3 ## No rescue on appeal Tessell asked the Federal Circuit for mandamus, an extraordinary order directing the Office to act. On February 24, 2026, the court refused in a nonprecedential order. In re Tessell, pp. 3–5 ## Three questions, not one For a company founded by or employing a patent’s inventors, the filing decision has three parts. A yes to the first doesn’t answer the other two. ## What to do Choose your side. ## Cuts the other way The forum split cuts both ways. Because the ITC statute allows “[a]ll legal and equitable defenses,” an inventor’s company could face assignor estoppel at the ITC on the same patent it is free to challenge at the PTAB. Athena Athena has been precedential as to § II.A only since 2013, but it predates the current discretionary-denial practice, under which a petition can be eligible and still be refused. Tessell is one order, so how often inventor involvement leads to denial isn’t measured. ## The takeaway Assess the risk of refusal before budgeting for the merits, and before treating an appeal as the fallback. ## Related stories - [Thirteen rulings, thirteen deciding facts.](https://postgrantproceeding.com/insights/d18-thirteen-rulings-thirteen-deciding-facts) - [Age starts the argument. It doesn’t end it.](https://postgrantproceeding.com/insights/d03-age-starts-the-argument-it-doesnt-end-it) - [A foreign government can’t petition. Prove you aren’t one.](https://postgrantproceeding.com/insights/d08-a-foreign-government-cant-petition-prove-you-arent-one) ## Sources - S27. Athena Automation Ltd. v. Husky Injection Molding Sys. Ltd., No. IPR2013-00290, Paper 18 (P.T.A.B. October 25, 2013) (precedential as to § II.A only). https://www.uspto.gov/sites/default/files/documents/Athena%20Automation%20Ltd.%20v.%20Huskey%20Injection%20Molding%20Systems%20Ltd.%20IPR2013-00290_Paper%2018.pdf - S28. Arista Networks, Inc. v. Cisco Systems, Inc., 908 F.3d 792 (Fed. Cir. 2018). https://www.cafc.uscourts.gov/opinions-orders/17-1525.opinion.11-9-2018.pdf - S29. Tessell, Inc. v. Nutanix, Inc., No. IPR2025-00298, Paper 17 (USPTO Acting Director Aug. 22, 2025). https://www.uspto.gov/sites/default/files/documents/IPR2025_00298_Paper_17.pdf - S30. In re Tessell, Inc., No. 2026-117 (Fed. Cir. Feb. 24, 2026) (nonprecedential order). https://www.cafc.uscourts.gov/opinions-orders/26-117.ORDER.2-24-2026_2652020.pdf - S13. Federal patent statutes, 35 U.S.C. §§ 253(a), 303(a), 311–315, 317 and 321–325. Reproduced in MPEP Appendix L (currency date stated by the appendix: Jan. 31, 2024). https://www.uspto.gov/web/offices/pac/mpep/mpep-9015-appx-l.html Precedential decisions bind the Board within their designated scope. Informative decisions show the Office’s reasoning but do not bind the Board. Court opinions are cited for what they decided; later history was checked on the date shown above. Updated - October 17, 2026: Athena is precedential only as to § II.A, as the USPTO list shows. The summary, the limits section, and the quiz now say so. General information about published decisions, not legal advice. Reading it does not create an attorney-client relationship.