In a ruling released on December 8, 2023, the Supreme Court of Justice of Ontario, Canada, agreed to certify a class action brought by persons who were exposed to Roundup, a glyphosate-based herbicide product manufactured by the American company Monsanto (acquired by the German company Bayer in 2018).

Certification is a necessary procedure in Canadian law to delimit the dispute and establish the class action. In a certification decision, the Canadian judge must determine whether: the motion is founded on a legal basis; there exists a class of at least 2 persons who can be represented by the plaintiff bringing the action; all members of the class action have common grievances; certification of a class action is a more efficient procedure for resolving all common grievances; and the representative plaintiff adequately represents the interests of the collective, is committed to the litigation process and has no conflict of interest with the other members of the collective. Once the class action has been certified, and the dispute delimited, anyone identified as a potential member of the same class action (same grievances, over a given period of time) can join it.

This request for certification has been initiated on behalf of all persons residing in Canada (excluding Quebec) who have suffered "significant exposure" to glyphosate-based products, having been distributed and sold across Canada since 1976 by Monsanto and its entities. The group includes people who have developed non-Hodgkin's lymphoma (and their relatives) or not. By "significant exposure", the complaint, as amended on February 11, 2021, means an application of Roundup on more than two occasions in a 12-month period and more than 10 times in a lifetime.

The complaint alleges that Monsanto knew or should have known that Roundup products and their active ingredient, glyphosate, are associated with an increased risk of developing and suffering from non-Hodgkin's lymphoma, that it failed to properly, adequately and fairly warn consumers of the risks associated with use and/or exposure to these products. Instead, the defendants engaged in years of bad faith activities to sow confusion and doubt in the public about the state of science on Roundup in order to preserve and increase their profits.

By March 4, 2020, the Walkers' action had been consolidated with Deblock's and transferred to the Ontario Superior Court of Justice.