The larger corporations importing via Mexico want Mexicans to be substituted wherever possible to replace American's in jobs...at the appropriate pay differential they are accustomed to. With Purchasing power parity being what it is, they can take the jobs for much less to oust the U.S. truckers whether they be union or non-union. And they will rather suddenly not just be doing the two-way traffic, but suddenly ALL the traffic all the time. Anybody who doesn't think that is possible or likely, I have a bridge for them to buy in Brooklyn.
Under the guise of trade, it is a wedge to commit wholesale labor arbitrage of an entire segment, and thence set precedents for other categories.
With the U.S. compelled to accept foreign replacement workers... on its own soil...it is not long for its existence. Gulliver needs to snap these strings and start a little constructive stomping around on the CFR/NAU apple-carts. NAFTA termination would be a good start.