(Reuters) - A new lawsuit accuses Conagra Brands ( CAG ) of deceiving consumers by "short weighting" its Mrs. Paul's and Van de Kamp's frozen fish products and falsely claiming they are "100% whole fish."

In a proposed class action filed on Tuesday in Chicago federal court, three consumers said Conagra artificially boosts the weight of 10 fish stick and fish fillet products by adding water and sodium tripolyphosphate, "which may then ooze out as a white goo" when cooked.

The consumers said sodium tripolyphosphate, a compound with commercial uses including in detergents, increases weight by an average 13%, causing them and others to overpay.

"A reasonable consumer has no reason to check what a product is composed of when the product labeling is replete with representations that it is '100% Whole Fish,' healthy, and caught in the wild," the complaint said

The U.S. Food and Drug Administration considers sodium tripolyphosphate safe. Tuesday's complaint calls it a suspected neurotoxin, registered pesticide and known air contaminant in large quantities, without providing the basis for those claims.

Conagra, based in Chicago, declined to comment on the lawsuit on Wednesday, saying it does not discuss pending litigation. Lawyers for the plaintiffs did not immediately respond to requests for comment.

The plaintiffs are William Martin of California, Catherine Foster of Massachusetts and Cindy Pappert of New York.

They are seeking unspecified damages for purchasers nationwide of the 10 Mrs. Paul's and Van de Kamp's fish products over the last four years, citing violations of California, Massachusetts and New York consumer production laws.

Conagra faces other litigation over its fish.

In March, a federal judge in Chicago refused to dismiss a lawsuit claiming it misled consumers into believing that nine Mrs. Paul's and Van de Kamp's products were sustainably sourced, including by calling them "Good for the Environment."

The case is Pappert et al v Conagra Brands Inc ( CAG ), U.S. District Court, Northern District of Illinois, No. 24-04835.