Two senators are proposing a new round of Iran sanctions aimed at preventing the Islamic republic from doing business around the world in euros.
Iran is already largely cut off from international transactions in dollars, meaning its business with foreign banks and customers must be conducted in other currencies.
And the budget amendment proposed by Republican Mark Kirk of Illinois and Democrat Joe Manchin of West Virginia targets what is being called the "euro loophole."
The amendment seeks to block Iran from accessing foreign holdings in euros and using the European Central Bank's interbank payment system.
Senators hope to vote on the budget this weekend. Dozens of amendments may not get a vote.