Here's a more clear statement of the Wisconsin legal authority:
Quote Quoting Wisconsin Statutes, Sec. 895.487 Civil liability exemption; employment references.
(1) In this section:
(a) "Employee" has the meaning given in s. 101.01 (3) and also includes a former employee.

(b) "Employer" has the meaning given in s. 101.01 (4).

(c) "Reference" means a statement about an employee's job performance or qualifications for employment and includes a statement about an employee's job performance or qualifications for employment provided pursuant to the settlement of a dispute between the employer and employee or provided pursuant to an agreement between the employer and employee relating to the termination of the employee's employment.
(2) An employer who, on the request of an employee or a prospective employer of the employee, provides a reference to that prospective employer is presumed to be acting in good faith and, unless lack of good faith is shown by clear and convincing evidence, is immune from all civil liability that may result from providing that reference. The presumption of good faith under this subsection may be rebutted only upon a showing by clear and convincing evidence that the employer knowingly provided false information in the reference, that the employer made the reference maliciously or that the employer made the reference in violation of s. 111.322.
Quote Quoting Gibson v. Overnite Transp. Co., 267 Wis. 2d 429;671 N.W.2d 388 (2003)
Wisconsin Stat. § 895.487(2) provides three ways in which the presumption of good faith may be rebutted: (1) "the employer knowingly provided false information in the reference," (2) "the employer made the reference maliciously," or (3) "the employer made the reference in violation of s. 111.322." The first option could arguably require actual malice because it requires that the employer act "knowingly." However, there remain two other options. The second option simply requires malice. The legislature was alerted to the ambiguity of the word "maliciously" but did not make any change. Common law prevails in Wisconsin until changed by statute. Aaby v. Citizens Nat'l Bank, 197 Wis. 56, 57, 221 N.W. 417 (1928). To abrogate the common law, the intent of the legislature must be clearly expressed, either in specific language or in a manner that leaves no reasonable doubt of the legislature's purpose. Sullivan v. School Dist. No. 1 Tomah, 179 Wis. 502, 506, 191 N.W. 1020 (1923). We therefore conclude that the legislature intended to keep the same standard of malice as existed in the common law-express malice.