Separation of powers.
The best resolution is that Congress may lay out various tariff rates and regimes, with the President able to defer to Congress or adopt his own plans and measures in reliance on his power over foreign relations. In a pinch, the President wins, unless Congress exercises its singular and peremptory power over the purse.
Unfortunately, since I do not have a seat on the Court, they may well come to a different and less sound resolution.
Separation of Ppwers would be an issue if congress had literally not created a bill that gave those powers to the president. The correct ruling would be congress can legislate a new bill revoking those powers, it is not justiciable.
That would be the legal ruling and if the court is not corrupted completely what would happen. I see this as a litmus test, if the court rules against Trump we know the shadow powers own it because this will be a full-on directive of the globalist to rule against Trump.