Wis. Stat. § 103.535: Unlawful conduct in labor controversies.

No person may picket, or induce others to picket, the establishment, employees, supply or delivery vehicles, or customers of anyone engaged in business, or interfere with the person’s business, or interfere with any person desiring to transact or transacting business with the person, when no labor dispute exists between the employer and the employer’s employees or their representatives.