The U.S. Food and Drug Administration has escalated a recall of several popular potato chip brands to its most serious classification due to the potential risk of salmonella contamination — a move that could affect hundreds of thousands of bags already on store shelves.

Manufacturer Utz issued a voluntary recall in May for various Zapp’s and Dirty potato chip products after discovering that a seasoning ingredient containing dry milk powder from a third-party supplier might be contaminated. An estimated 650,000 bags with best-by dates from July 27 to August 31 were believed to be impacted.

In its latest enforcement report released Friday, the FDA upgraded the recall to Class 1 status, reserved for situations where there is a “reasonable probability” that consumption could cause serious adverse health consequences or death.

While Utz has emphasized that no salmonella has been detected in its products and no illnesses have been reported, the FDA’s highest-risk classification underscores the potential danger. Salmonella is a leading cause of foodborne illness worldwide, with symptoms including fever, stomach pain, diarrhea, nausea, and vomiting.

The recall affects multiple varieties, including Bayou Blackened Ranch, Salt and Vinegar, Big Cheezy, and Sour Cream and Onion flavors. Consumers are urged to check their pantries and discard any affected bags, with refunds available through Utz.

This incident highlights ongoing challenges in the food supply chain, particularly with third-party ingredients, and serves as a reminder for shoppers to stay vigilant about recalls. For those who may have consumed the products, experts recommend monitoring for symptoms and seeking medical attention if needed.