Wis. Stat. § 13.66

Except as authorized under s. 13.621, no person may engage in lobbying as a lobbyist unless the person has been licensed under s. 13.63 and has been authorized to act as a lobbyist for the principal whom the lobbyist represents under s. 13.65. Except as authorized under s. 13.621, no principal may authorize its lobbyist to engage in lobbying until the lobbyist is licensed and the principal is registered under s. 13.64.