Ryan said the US needs to address concerns about the things that he said Tehran would do with any financial access gained in the wake of the nuclear deal it has sealed with the P5+1.
"This is one of the reasons I adamantly oppose any steps this administration may take to give Iran access to the dollar," Reuters has quoted him as telling reporters at a weekly press conference.
A top US official has said that Iran is not gaining access to US financial system, Reuters added.
The media had earlier reported in late March that the administration of US President Barack Obama is working on a plan to allow dollars to be used in doing business with Iran.
The Associated Press said in a report that the Obama administration may soon tell foreign governments and banks they can start using the dollar in some instances to facilitate business with Iran in what could provide Iran with the best of the removal of the US-led sanctions.
The AP has quoted unnamed officials as saying that the Treasury Department is considering issuing a general license that would permit offshore financial institutions to access dollars for foreign currency trades in support of legitimate business with Iran.
US banks are still banned from dealing with Iran as part of an old US trade embargo that still remains in place. Accordingly, this is believed to have already effectively blocked any transactions with Iran which is based on US dollars because they would ultimately have to be cleared in the US.
Indications had been specifically growing lately that a legacy of hefty fines by the US on banks that are caught for violating Iran sanctions is deterring businesses from trading with Iran.
Reuters in a recent report warned that corporate leaders have already become frustrated over this even though the sanctions removal against Iran would have naturally meant the doors are open for investments in Iran.