Can someone be stopped from filing repeated lawsuits in Ontario courts?

Yes. Ontario courts have authority to declare a person a vexatious litigant and require them to obtain court permission before starting or continuing any new legal proceedings. This order is available under Ontario's Courts of Justice Act and is typically sought when a person has repeatedly brought frivolous or vexatious proceedings that abuse the court process or harass the opposing party.

Courts do not declare someone vexatious lightly. The test looks at the pattern of conduct: repeated unsuccessful claims on the same or related issues, bringing proceedings for improper purposes, or using the courts to harass rather than to vindicate a genuine right. A single unsuccessful lawsuit does not make someone vexatious.

If you are being harassed through repeated baseless lawsuits, you can bring a motion to have the other party declared vexatious. If such an order is granted, the declared person must obtain a judge's permission before filing any new proceeding, and permission will only be granted if the proposed proceeding is not an abuse of process.