Wis. Stat. § 11.1107: Limitation on cash contributions.

Every contribution of money exceeding $100 shall be made by negotiable instrument or evidenced by an itemized credit card receipt bearing on the face the name of the remitter. No committee required to report under this chapter may accept a contribution made in violation of this section. The committee shall promptly return the contribution, or donate it to the common school fund or to a charitable organization in the event that the donor cannot be identified.