Wis. Stat. § 766.15: Responsibility between spouses.

(1) Each spouse shall act in good faith with respect to the other spouse in matters involving marital property or other property of the other spouse. This obligation may not be varied by a marital property agreement.

(2) Management and control by a spouse of that spouse’s property that is not marital property in a manner that limits, diminishes or fails to produce income from that property does not violate sub. (1).