Wis. Const. art. XIII, § 11

No person, association, copartnership, or corporation, shall promise, offer or give, for any purpose, to any political committee, or any member or employe thereof, to any candidate for, or incumbent of any office or position under the constitution or laws, or under any ordinance of any town or municipality, of this state, or to any person at the request or for the advantage of all or any of them, any free pass or frank, or any privilege withheld from any person, for the traveling accommodation or transportation of any person or property, or the transmission of any message or communication. No political committee, and no member or employee thereof, no candidate for and no incumbent of any office or position under the constitution or laws, or under any ordinance of any town or municipality of this state, shall ask for, or accept, from any person, association, copartnership, or corporation, or use, in any manner, or for any purpose, any free pass or frank, or any privilege withheld from any person, for the traveling accommodation or transportation of any person or property, or the transmission of any message or communication. Any violation of any of the above provisions shall be bribery and punished as provided by law, and if any officer or any member of the legislature be guilty thereof, his office shall become vacant. No person within the purview of this act shall be privileged from testifying in relation to anything therein prohibited; and no person having so testified shall be liable to any prosecution or punishment for any offense concerning which he was required to give his testimony or produce any documentary evidence. Notaries public and regular employees of a railroad or other public utilities who are candidates for or hold public offices for which the annual compensation is not more than three hundred dollars to whom no passes or privileges are extended beyond those which are extended to other regular employees of such corporations are excepted from the provisions of this section.