Wis. Stat. § 285.15: Interstate agreement.

After May 14, 1992, the governor may enter into an agreement with the governor of the state of Illinois, that may also include the governors of the states of Indiana and Michigan, that specifies measures for the control of atmospheric ozone that are necessary in order to implement an interstate ozone control strategy to bring an area designated under 42 USC 7407 (d) as an ozone nonattainment area into attainment with the ambient air quality standard for ozone if the area includes portions of this state and the state of Illinois.