From our leather supplier, Wickett & Craig:

While we do not believe there are any chemicals within our Veg Tanned leather that fall under Proposition 65, it is virtually impossible to be 100% certain. There are over 900 chemicals listed by California under Proposition 65. To err on the side of caution, we are posting this warning:

CALIFORNIA PROPOSITION 65 WARNING: This can expose you to chemicals including lead. which is known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information go to P65Warninqs.caqov.