We get this question frequently, so we will drop a few lines here to refer people back to. Currently, there are two states that prohibit drivers from putting suction cup mounts on their windshield while operating their vehicle– California and Minnesota. Want to find out exactly what the restriction is and what your alternative mounting options are?
The Laws

In California, you will want to refer to Vehicle Code Section 26708(a) for all of the details. In Minnesota, you will want to refer to Section 169.71 for the details. These outline what you can and cannot mount on your windshield as well as visibility requirements.