Wis. Stat. § 29.311: Shotshell restrictions.

(1) No person may hunt waterfowl or coots with any firearm or airgun using any shotshell classified by the federal government as toxic or harmful to wildlife or the environment.

(2) The department may not limit the use, possession, or control of shot shells on the basis of the size of the contained shot for the hunting of a fur-bearing animal during an open season established for that animal by the department or for the hunting of an animal as provided under s. 29.337 (1).