Wis. Stat. § 175.09: Standard time.

(1) The standard of time in this state shall be the solar time of the ninetieth meridian west of Greenwich, commonly known as central time, and no department of the state government, and no county, city, town or village shall employ any other time, or adopt any ordinance or order providing for the use of any other than the standard of time.

(2) No person operating or maintaining a place of business of whatsoever kind or nature, shall employ, display or maintain or use any other than the standard of time in connection with such place of business.

(3) Whoever shall in connection with any place of business use any other than the standard of time shall be fined not less than $25 nor more than $500 or imprisoned for not less than 10 days nor more than 30 days or both.