Supreme Court Of Canada Broadens The Scope Of “Material Change”

• Published date: 27 April 2026
• Subject Matter: Corporate/Commercial Law, Privacy, Data Protection, Privacy Protection, Securities
• Law Firm: Bennett Jones LLP
• Author: Mr Douglas Fenton, Marshall Torgov and Kanwar Brar (Articling Student)

The Supreme Court of Canada's much anticipated decision in Lundin Mining Corp. v. Markowich, 2025 SCC 39 clarifies the definition of “material change” under securities law, providing long-awaited guidance on when public issuers must disclose information to the market and adopts a broad interpretation of what constitutes a “material change”. The decision will have broad implications for public companies and their directors and officers attempting to navigate disclosure decisions in real-time.

The Supreme Court also addressed a secondary issue: the test for leave to commence an action (including a proposed class action) for secondary market misrepresentation. The leave test is a “preliminary merits” assessment, requiring the plaintiff to show that the action is brought in good faith and that there is a reasonable possibility of success at trial. As a result, the Supreme Court's decision is expected to have implications for the viability of secondary market misrepresentation class actions in Canada and may contribute to an increase in secondary market misrepresentation claims.

The Decisions Below

In Lundin, the central issue was whether pit wall instability and a rockslide at a major copper mine operated by Lundin Mining Corporation in Chile was a “material change” requiring prompt disclosure under the Ontario Securities Act. Lundin disclosed the rockslide approximately one month after the incident, as part of a regular news release containing operational updates. Lundin's disclosure, which was coupled with revised financial forecasting, resulted in an immediate 16% decline in its share price.

The plaintiff, a retail investor, initiated...