Wis. Stat. § 133.05: Secret rebates; unfair trade practices.

(1) The secret payment or allowance of rebates, refunds, commissions or unearned discounts, whether in the form of money or otherwise, or the secret extension to certain purchasers of special services or privileges not extended to all purchasers purchasing upon like terms and conditions, such payment, allowance or extension injuring or tending to injure a competitor or destroying or tending to destroy competition, is an unfair trade practice and is prohibited.

(2) No person may induce, solicit or receive anything of value which is prohibited under sub. (1).

(3) Any person knowingly violating this section may be fined not more than $25,000 or imprisoned in the county jail for not more than one year or both.

(4) As an alternative to the criminal penalty for violation of this section, the department of justice or district attorney may bring an action for a civil forfeiture. In an action for a civil forfeiture under this subsection a person who violates this section may be required to forfeit not more than $25,000.

(5) This section does not apply to the insurance business.