Broccoli florets Walmart stores in 20 states have been under a recall since late last year. The FDA now has updated its recall notice for Marketside Broccoli Florets to Class I, meaning the product could be potentially deadly.

Last year, California-based grocery producer Braga Fresh voluntarily issued a precautionary recall of 12-ounce washed and ready-to-eat Marketside Broccoli Florets sold at more than 1,000 Walmart stores due to the possibility of Listeria monocytogenes contamination.

The U.S. Food and Drug Administration has labeled the broccoli recall as a Class I, the highest risk level issued by the agency.