Steve's barking; If the U.S. Congress votes against the Iran deal.

Now let me get this straight, right now we have sanctions against Iran to stop it from developing the bomb as in nuclear.
The negotiation lifting the sanctions so that Iran can be inspected as to not be building the bombs is to go to the UN.
Now This is what I'm trying to understand, if the UN says it's yes but the U.S. Congress says no, every country under the sun except the U.S. can trade with Iran. The U.S. would no say in the
inspections of Iran, now that doesn't seem very bright to me.
What happens to our companies who want to trade with Iran? Are they left out in the cold, or do they us their foreign subsidiaries and to paraphrase a character on Steinfeld (the soup nazi) no tax for you.