Wis. Stat. § 134.06
It shall be unlawful for any chauffeur, driver or other person having the care of a motor vehicle for the owner to receive or take directly or indirectly without the written consent of such owner any bonus, discount or other consideration for supplies, or parts furnished or purchased for such motor vehicle or upon any work or labor done thereon by others or on the purchase of any motor vehicle for the chauffeur's, driver's or other person's employer and no person furnishing such supplies or parts, work or labor or selling any motor vehicle shall give or offer any such chauffeur or other person having the care of a motor vehicle for the owner thereof, directly or indirectly without such owner's written consent, any bonus, discount or other consideration thereon. Any person violating this section shall be guilty of a misdemeanor and punished by a fine not exceeding $25.
Wis. Stat. § 134.06