Iowa Code § 321.476: Stopping, weighing, and inspecting vehicles by state patrol.

1. A member of the state patrol of the department of public safety is authorized to do any of the following:

a. Stop any motor vehicle or trailer on the highways for the purposes of weighing and inspection, to weigh and inspect the same and to enforce the provisions of the motor vehicle laws relating to the registration, size, weight, and load of motor vehicles and trailers.

b. Weigh and inspect vehicles which have moved from a highway onto private property under circumstances which indicate that the load of the vehicle, if any, is substantially the same as the load which the vehicle carried before moving onto the private property.

2. Any person who prevents or in any manner obstructs an officer attempting to carry out the provisions of this section is guilty of a simple misdemeanor.