The measure passed 99 to 0 just weeks after the House passed it 419-1. It will be sent to President Barack Obama
, who has not said if he will sign or veto the legislation.
"Preserving these sanctions is critical given Iran's disturbing pattern of aggression and its persistent efforts to expand its sphere of influence across the Middle East," Senate Majority Leader Mitch McConnell said this week.
"Extending the Iran Sanctions Act is an important step in congressional efforts to keep Iran's feet to the fire on a host of issues. Doing so it particularly vital if the United States is to retain a credible deterrent of snap back sanctions if Iran cheats" on the nuclear accord," said Sen. Ben Cardin of Maryland, the top Democrat on the Foreign Relations Committee.
The sanctions, which target Iran's energy, military and banking sectors, were first put in place in 1996 and have been extended and added to since then. Many lawmakers believe it was these congressionally-mandated sanctions that forced Iran to the bargaining table and led to an eventual nuclear agreement.
The sanctions are actually not in effect at the moment since the Obama administration is allowed to waive them as long as Iran is in compliance. But lawmakers were still anxious to keep the sanctions -- which otherwise would expire at the end of the year -- in law so Iran understands how serious Congress is that the Islamic state not try again to develop nuclear weapons.
The action comes weeks before the end of the Obama administration, which spent years negotiating the deal, and the beginning of the Trump administration, which has warned it might scrap the deal altogether. There have been signs in recent days Trump might not ditch the accord but might use other steps to apply pressure on Iran to stop its support of international terrorism, its development of ballistic missiles, and its human rights abuses.
"I expect that next year the new Congress and new administration will undertake a review of our overall policy toward Iran, and these authorities should remain in place as we address how best to deal with Iranian missile tests, support to Hezbollah and the Syrian regime," McConnell said.
Iran is not happy about the extension, believing it violates the international accord. Supreme Leader Ayatollah Ali Khamenei said last week his country would respond.
"If this sanction is implemented, this is definitely a violation of the agreement, without any doubt," Khamenei said in an address on state television. "And they should know that the Islamic Republic will definitely react towards it."
The White House has argued against Congress extending the sanctions, arguing it has the authority already to unilaterally re-impose the sanctions if needed. The White House has stopped short of saying if the President will veto the measure. If he did, based on the vote counts in each chamber, Congress could easily override the veto.