Patent Infringement and Limitation Periods

Claims for infringement of a patent have an unusual place when it comes to limitation periods. A recent decision of the Alberta Court of Appeal has provided some clarity to this issue but there is still uncertainty as to limitation periods for infringement claims.

Most provinces have legislation that impose a limitation period on claims. For example, in Ontario, the Limitations Act provides that, “a proceeding shall not be commenced in respect of a claim after the second anniversary of the day on which the claim was discovered.” Similarly, in Alberta, “if a claimant does not seek a remedial order within … 2 years after the date on which the claimant first knew, or in the circumstances ought to have known that the injury for which the claimant seeks a remedial order had occurred … the defendant, on pleading this Act as a defence, is entitled to immunity from liability in respect of the claim.” In other words, if a party is aware of a potential claim, it shouldn’t wait more than two years from when it became aware of the claim to start a proceeding.

For patent infringement claims, there are three aspects which add an interesting wrinkle:

1. Frequently, the infringement is ongoing. There are multiple acts of infringement, so while a patentee may have been aware of an act of infringement more than two years ago, there was also an act of infringement yesterday when further sales were made that is within the two year limitation period.
2. Most patent infringement cases are brought in the Federal Court and the Federal Courts Act provides for “the laws relating to prescription and the limitation of actions” to apply for causes of action arising in a province, otherwise a proceeding shall be taken within six years after the cause of action arose – see section 39.
3. The Patent Act has a section that relates to recovery of remedies for patent infringement. Section 55.01 states that, “No remedy may be awarded for an act of infringement committed more than six years before the commencement of the action for infringement.” The Patent Act’s section 55.01 is often referred to as a “six-year limitation period” but as we will see, this provision of the Patent Act is structured differently than a typical limitation period.

Another consideration is that there can be related claims, other than patent infringement claims, to which section 55.01 does not apply. For example, claims for misappropriation of trade secrets, ownership and related claims may be caught by the provincial limitation periods, and not covered by the Patent Act.

If a defendant is continuing to sell infringing products, then arguably the limitation period applies for each sale. So even if the patentee was aware of infringement for more than two years, it can still bring a proceeding for patent infringement for current sales. It may be less clear how a limitation period applies to past sales, such as those that took place more than two years before a claim was started.

In JL Energy Transportation Inc v Alliance Pipeline Limited Partnership, 2025 ABCA 26, the court considered the limitation period for alleging breach of a patent license agreement and patent infringement. The court held that the provincial limitation period does not apply to causes of action created by federal statutes which are subject to a discrete limitation period, such as claims for patent infringement: “appellant’s claim for patent infringement is subject to the limitation period in s. 55.01 of the Patent Act.” (at [32]).

The full panel in JL Energy referred to the case of Secure Energy Services Inc. v Canadian Energy Services Inc., 2022 ABCA 200 in which a limitation period was found to apply to claims of patent ownership. This was a case I was involved in where the defendant to a patent infringement proceeding had counterclaimed for ownership of the asserted patent and these claims were found to be outside the applicable Alberta limitations period.

In JL Energy, for the breach of the license agreement, the court said that this allegation was mostly raised to address a potential defence from the defendant. The defendant could argue that there was no patent infringement because its actions were covered by a license. The court concluded at [42] that, “those breaches [of the license] would likely be concurrent with breaches that are actionable under s. 55 [of the Patent Act], and more robust remedies may be available for the infringement claim.”

Limitation periods for patent infringement were also discussed by the Federal Court in Paid Search Engine Tools, LLC (PSET) v. Google Canada Corporation, 2020 FC 992 aff’d on other grounds 2021 FCA 63, which held that “the discoverability principle applies to section 55.01 of the Patent Act” including facts about when the patentee learned of the alleged infringement and was able to begin an action. In PSET, the dispute was over whether pre-grant ‘reasonable royalties’ could be claimed outside the 6-year period of section 55.01. The Federal Court of Appeal dismissed the appeal on procedural grounds as part of the determining a question of law prior to trial and expressed “no view” on discoverability. Prof Siebrasse had some helpful commentary on this decision where he discusses how the typical limitation period runs forward from a triggering event, while section 55.01 runs backward from a triggering event, the starting of the action.

Section 55.01 of the Patent Act reads as limiting remedies, rather than limiting the initiation of a proceeding, unlike provincial limitation periods, or the cross-border limitation period of the Federal Courts Act.

Whether section 55.01 is a true limitation period in the sense of provincial limitation periods, will likely need to be litigated in the appropriate case. Some patentees have brought actions patent infringement after the patent has expired which could also raise novel limitation period arguments. A patentee that is aware of infringement, watches infringement grow over many years should carefully consider whether initiating an action sooner (to capture an earlier period of infringement) is preferred over waiting to bring an action and facing potential limitation period challenges.