Any business impacted by the tariffs will have standing to go to federal court and argue that trade practices accepted for a century by legislatures and administrations of both parties do not constitute "unequal impositions" under the intended meaning of the statute.

They'd have to argue something other than that. There could be a standing regulation that says "Ships carrying any American goods must pay 30% higher docking fees"; if that had been accepted for a century, it would still be a slam dunk case of "unequal impositions".