Can You Intervene in an Ontario Anti-SLAPP Motion?

What is an anti-SLAPP motion and why does it matter?

An anti-SLAPP motion is a legal tool that lets a defendant ask a court to dismiss a lawsuit early when the claim appears designed to silence public participation rather than address a genuine wrong. Ontario’s Courts of Justice Act, section 137.1, gives defendants this right. If the motion succeeds, the lawsuit is thrown out before trial and the plaintiff may have to pay costs. These motions come up most often in defamation cases where the defendant argues their speech touched on a matter of public interest.

Can a third party intervene in an anti-SLAPP motion in Ontario?

Yes, a third party can apply to intervene in an anti-SLAPP motion, but the court has wide discretion to say no — and in this case, it did. In Dattani v. Lantsman et al., 2026 ONSC 3379 (CanLII), the court dismissed motions brought by proposed interveners who wanted to participate in an ongoing anti-SLAPP hearing. The judge found that the proposed interveners were unlikely to make a useful contribution and that allowing them in would cause real prejudice to the defendants.

Under Rule 13 of Ontario’s Rules of Civil Procedure, a person or organization can seek leave to intervene either as a party or as a friend of the court (amicus curiae). The test is whether the proposed intervener has a genuine interest in the outcome and whether their participation would actually help the court — without unfairly burdening the existing parties.

Does section 137.1(5) of the Courts of Justice Act block interventions on anti-SLAPP motions?

No — the court rejected the argument that section 137.1(5) automatically bars all interventions. That provision restricts certain procedural “steps in the proceeding” once an anti-SLAPP motion is brought. The judge drew a careful distinction: steps within the motion itself are different from steps in the broader proceeding. An intervention application is a step within the motion, not a step in the proceeding as a whole, so the statutory prohibition does not automatically apply. The court also noted that interventions have been permitted on anti-SLAPP motions and appeals in earlier cases.

This is an important clarification. It means the door is not legally closed to interveners, but getting through that door still requires satisfying the Rule 13 test — which is genuinely difficult, especially in private defamation cases.

Why were the intervention requests denied here?

The proposed interveners ran into several practical problems. First, the motions were brought very late — sometimes called “eleventh hour” applications — right before the scheduled hearing. Second, allowing them to participate would have expanded the evidentiary record, adding material the defendants had no reasonable opportunity to address. Third, the court distinguished this situation from constitutional or public law cases, where interveners regularly add value by raising systemic arguments that individual parties cannot. In a private defamation lawsuit — even one with public interest elements — the court found the existing parties were fully capable of making the relevant arguments themselves.

The judge’s message was clear: the fact that a case touches on public interest issues does not automatically transform it into the kind of case where outside voices are needed or welcome.

Who goes first when defendants bring an anti-SLAPP motion?

The defendants go first. The court ordered that the moving defendants present their arguments first and address all issues on the anti-SLAPP motion. This might seem counterintuitive — usually the party who brings a motion speaks first, and defendants are the moving parties here. But the judge considered the plaintiff’s own concession that the public interest threshold was met, which shifted the practical burden. The court also drew on practice in defamation trials, where defendants traditionally lead. The result is a logical sequence: defendants lay out their case for dismissal, then the plaintiff responds.

This procedural point matters for anyone planning or defending an anti-SLAPP motion in Ontario. Knowing the expected order of argument helps counsel prepare and manage hearing time effectively. Our Ontario litigation lawyers can help you navigate these procedural rules from the outset.

How is this case different from constitutional or public law interventions?

Courts routinely allow interveners in constitutional cases because those decisions bind everyone, and outside perspectives genuinely help. A ruling that a law is unconstitutional affects the whole public, not just the two parties in court. Private defamation actions are different — even when the speech at issue is about a public figure or a matter of public debate, the legal outcome primarily affects the plaintiff and the defendant. The court in this decision drew that line clearly, signalling that organizations hoping to ride along on high-profile defamation cases will face a high bar.

Practical takeaways for anyone involved in Ontario defamation litigation

• Move early if you want to intervene. Last-minute intervention requests face an uphill battle. Courts treat timing as a serious factor, and an eleventh-hour application signals potential prejudice to the parties who have been preparing for months.
• Useful contribution is the key test. Ask honestly whether you can add something the existing parties cannot. If the plaintiff and defendant can make all the relevant arguments, a court will likely say no.
• Section 137.1(5) is not an absolute bar, but it is not irrelevant. The prohibition on steps in the proceeding does not automatically kill an intervention application, but courts will scrutinize whether your participation disrupts the anti-SLAPP process.
• Defendants argue first on anti-SLAPP motions. If you are a defendant planning an anti-SLAPP motion, expect to lead the hearing and address every issue — build your materials accordingly.
• Public interest elements do not automatically open the door. A case involving public figures or public debate is not the same as a constitutional case. The intervention rules are applied more strictly in private litigation.

If you are facing a defamation claim or considering an anti-SLAPP motion in the Hamilton or Burlington area, our litigation lawyers serving Burlington and the surrounding region are available to help you understand your options at every stage of the process.

UL Lawyers offers a free initial consultation from our Burlington office and works with clients across Ontario. Whether you are a plaintiff, a defendant, or a third party wondering about your rights, reach out to our civil litigation team to discuss your situation.

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This article is automated commentary on a public court decision and is for general information only — not legal advice. Decisions rely on facts unique to each case. If you are affected by a similar issue, contact a lawyer for advice specific to your situation.