Wis. Stat. § 13.36

The compensation of all witnesses who are subpoenaed and appear pursuant to s. 13.31 shall be $2 for each day’s attendance and 10 cents per mile, one way, for travel to attend as such witness. The department of administration shall audit the accounts of such witnesses upon the certificate of the chairperson of the committee before which any such witness has attended, stating the number of days’ attendance and the distance the witness has traveled, and the accounts so audited shall be paid out of the state treasury and charged to the appropriation for the legislature.