The US Congress has overwhelmingly approved new sanctions against foreign companies that trade with Iran, over its nuclear programme.
Those firms that supply Iran's Revolutionary Guards or contribute to the country's energy industry are targeted by the bill.
The sanctions are designed to put pressure on Tehran which denies seeking to acquire nuclear weapons.
The bill now goes back to President Barack Obama to be signed into law.
The Senate and House of Representatives acted in quick succession on Thursday to agree to the new penalties. The Senate vote was 99-0 and the House vote was 408-8.
Iran says its nuclear industry is for peaceful purposes.
'No both ways'
"We must stop Iran from developing a nuclear weapon, a weapon that would surely threaten the national security of the United States and of Israel," said Democratic Senate Majority Leader Harry Reid.
Republican Senator John McCain said: "We will be posing a choice to companies around the world: Do you want to do business with Iran? Or do you want to business with the United States?
"We don't think that is much of a choice, but we will force companies to make it. They can't have it both ways."
Earlier this month, the UN Security Council voted to impose a fourth round of sanctions on Tehran for failing to halt its nuclear enrichment programme.
They include tighter finance curbs and an expanded arms embargo, but not the crippling sanctions the US had wanted.
Three earlier rounds of UN sanctions have blocked trade of "sensitive nuclear material", frozen the financial assets of those involved in Iran's nuclear activities, banned all of Iran's arms exports and encouraged scrutiny of the dealings of Iranian banks.