They are tring to force anyone with a truck an trailer at 10,000 combined gross weight to comply with all the regulations that over the road truckers have to follow. There is a whole giant book full of rules, it is CFR49. Do a google search on cfr49 to see it.
If you have your vehicles tagged in a company name, if you have company or sponsor names on the truck or trailer, if you admit that you can win any money at the show/race that you are going to, they call it "commerce" and nail you.