Wis. Stat. § 346.59: Minimum speed regulation.

(1) No person shall drive a motor vehicle at a speed so slow as to impede the normal and reasonable movement of traffic except when reduced speed is necessary for safe operation or is necessary to comply with the law.

(2) The operator of a vehicle moving at a speed so slow as to impede the normal and reasonable movement of traffic shall, if practicable, yield the roadway to an overtaking vehicle and shall move at a reasonably increased speed or yield the roadway to overtaking vehicles when directed to do so by a traffic officer.