This part must contain a chemical that is listed on the California Proposition 65 list of chemicals. Once a chemical is listed, manufacturers have to provide a warning if the chemical is present in the item for all products sold in California. Even if the chemical is present in such a small amount that you could wear the item, eat off it and sleep on it 24 hours a day and still not be exposed enough to even have an elevated risk factor, you must either remove it or label your product.
It gets even better in that the law also allows for anyone to sue for the good of the people of the State of California. This alone has spawned a nice little industry for law firms. There are a group of "bounty Hunter" firms that do nothing but sue based on this law. They make millions each year.
This label isn't anything to do with import verses domestic made product. In my experience most imported items that contain listed chemicals are not labeled at all. The ability to sue a Chinese manufacturer is pretty much non existent.
You may well start seeing many more items with these labels as California recently listed a new plasticizer. This is the material in plastic that gives it flexibility. This new listing is on pretty much the main workhorse chemical in a vast majority of flexible items. Plasticizers use a Phthalate. This phthalate is what is causing the listing. Lead has been on the list for a long time and the bounty hunters have sued just about everyone that might have lead in their product.
If you are interested you can google "prop 65" and see for yourself what a fine piece of legislation it is. You can also see the list of chemicals. Believe it or not sawdust is one of the items on the list.
Sorry for the rant but, lets just say that I am more familiar with this topic then I would like to be.
Remnar