"We" give them the right, USA cannot stop a bank transacting with X or X company in Iran, Cuba, etc. but since USA owns the USD they can block these banks from using/clearing USD which is a lethal blow for a bank. But if USA gets on the wrong side of this and countries start phasing out $ and start favouring € (this is a 50 year process btw) then USA will have an empty threat in its hands. And I do know that there many connecting points/sanctions that can be imposed, not just the currency.