There has been much bad PR surrounding the takings cases associated with NAFTA and Mexico doesn't want any bad PR on trucking so they have jumped thru the hoops. All the inspection stations have been built. As to whether they would actually sue, eventually they would. In the mean time, they could retaliate. As you may have read, the prearranged NAFTA date for allowing US produce into Mexico is rapidly approaching. The Mexicans could say: if you don't let our trucks in, we won't let your produce in. This would be a major loss to the US.