A new report from the U.S. Public Interest Research Group (U.S. PIRG) Education Fund says Playskool crayons sold at Dollar Tree and on Amazon may contain asbestos.

U.S. PIRG’s annual School Supplies Shopping Guide says trace amounts of asbestos were found in the Playskool crayons sold at Dollar Tree. According to the CDC, individuals exposed to asbestos can develop several life-threatening conditions, including lung cancer and mesothelioma.

“Based on our testing, we know that most manufacturers make safe school supplies. We’re calling on the makers of unsafe products to get rid of toxic chemicals and protect American schoolchildren,” said Kara Cook-Schultz, U.S. PIRG Education Fund Toxics Director. U.S. PIRG is a nonprofit, nonpartisan organization that conducts consumer-based research.

According to a report from the Washington Post, Playskool’s parent company, Hasbro, said it is conducting a thorough investigation into the matter. Dollar Tree executives said independent tests have indicated that its crayons do not contain asbestos.

U.S. PIRG tested six other brands of crayons and did not find asbestos or other toxic substances.