Maybe because of material content: http://www.apparelandfootwear......tances.asp
Restricted Substances List (RSL) American Apparel and Footwear Association:
"California Proposition 65 requires labeling for products containing chemicals known to the state to cause cancer. Typically labeling requirements are dependent on consumer exposure to the chemical, not the concentration in the product. Exposure levels have been determined for certain chemicals under certain applications, products, or use through legal settlements in the State of California. Ingredients for which there have been legal settlements are included on the list."