A popular brand of crayons contains toxic levels of asbestos, according to a consumer advocacy group that is calling on retailers like Dollar Tree and Amazon.com to pull them from their shelves.

The U.S. Public Interest Research Group Education Fund says Playskool crayons tested positive for asbestos, which can lead to lung cancer and mesothelioma if inhaled or ingested. The group tested 36-packs of crayons purchased at a Dollar Tree store in Chicago but noted that they are also being sold online at Amazon, eBay and DollarDays.com.

A spokeswoman for Playskool’s parent company, Hasbro, said it is conducting a “thorough investigation” into the claims. Leap Year Publishing, the Massachusetts-based manufacturer of the crayons, said it is also reviewing its lab tests.

Although federal laws regulate the amount of asbestos in drinking water, schools and some consumer products, there are no regulations on the amount of asbestos allowed in children’s products, according to Cook-Schultz.

The group also tested five other crayon brands – Crayola; Target’s Up & Up; Cra-Z-Art; Disney Junior Mickey and the Roadster Racers; and Roseart – that were found to be asbestos-free.