That's bad news for the cannabis industry, which has turned to billboards as a marketing opportunity.
Cannabis companies have precious few options when it comes to advertising. With the federal government still listing marijuana as an illegal drug, the industry faces strict regulations on advertising its products and services.
The situation has left companies scrambling to get around advertising restrictions. One outlet for companies has involved placing cannabis billboards on highways in states with legal weed. But earlier this year, California officials mandated the removal of some billboards. And proposed action in Michigan could signal that idea is taking hold in other locations.