Trucks from Mexico are exempt ...
That's funny. Soon, trucks from Canada will be exempt too.
My prediction? This law will "evolve" as all bad legislation does. At some point, it will have to exempt out of state trucks and trailers that are interstate carriers. So then it would only apply to companies based in CA. They won't see the bullet in the barrel that they are looking into and CA will completely decimate it's own trucking industry (the perverbial shooting thyself in the head).
You will see out of state carriers start to truck to and from the ports from out of state. Companies will then start avoiding the CA shipping ports and opt for Oregon and Washington or even East Coast and Mexico.
Our Fed sees no conflict with the Constitutions interstate commerce clause here even though this is one of the few reasons that a Federal Government was argued for by the Federalists.