Some experts here warn, however, that the sanctions also could harm Iranian civilians and companies from other countries doing business with Tehran.  The House of Representatives passed the bill 408-8 and sent it to President Barack Obama for signing into law.

The Senate had approved it 99-0 earlier in the day. By passing this vote, Congress hopes to pressure Tehran into curbing its nuclear program, which Washington suspects is aimed at making a bomb. The last few weeks have seen momentous developments with regard to Iran. With the support of 25 countries, including all five permanent members of the UN Security Council, the IAEA voted to censure Iran for its unwillingness to be fully transparent over its nuclear ambitions.

In addition, turmoil stemming from Iran’s post-election crisis this summer has continued, with protests taking place on a scale not seen since the election itself. US lawmakers from both parties have been pushing for months to tighten US sanctions on Iran. At the Obama administration’s request, however, they held off until the UN Security Council and the European Union agreed on new multilateral sanctions. But the lawmakers then declared that still tougher measures were needed.

Congressman Howard Berman has admitted that the sanctions bill could have an impact on the average Iranian, calling it a “distasteful prospect.” In a recent piece for Think Progress Matt Duss elaborated on how the Congressional sanctions would have an adverse effect on the Iranian people, particularly the Green Movement. Duss noted that “in September, Mir Hussein Mousavi said sanctions will impose agonies on a nation who suffers enough from miserable statesmen.”

“It will certainly not change the calculations of the Iranian leadership overnight, nor is it a panacea,” William Burns, under-secretary for political affairs at the State Department, said of US-backed sanctions passed by the UN Security Council earlier this month during testimony Tuesday before the Senate Foreign Relations Committee.

“But it is a mark of the potential effect that Iran has worked so hard in recent months to avert action in the Security Council and tried so hard to deflect or divert the steps that are now under way.”

The Obama administration failed to get US lawmakers to make blanket exemptions for countries that are cooperating with multilateral efforts to isolate Iran.

The legislation only allows the president to waive the new sanctions on companies from “cooperating” countries on a case-by-case basis, for 12 months.

But even this waiver was too lenient for some House Republicans, who worried Obama will use it.

“The many companies from China and elsewhere, rapidly building Iran’s energy facilities today, will be surely exempted from these sanctions,” said Representative Ed Royce, who still voted for the bill.

“Because of this legislation, we will be posing a choice to companies around the world. Do you want to do business with Iran, or do you want to do business with the United States?” Republican Sen. John McCain said during Senate debate.

US companies are already prohibited from doing business with Iran. Foreign companies with big investments in Iran’s energy sector also can be sanctioned under current US law. But many US lawmakers say this has not been enforced.

Some companies such as Italy’s oil and gas company Eni and French energy giant Total have been backing away from business with Tehran amid the US drive to isolate Iran.

But other companies are still in business with Iran or considering it. Russia and China, which have strong economic ties with Tehran and have at times resisted sanctions, supported recent U.N. sanctions. Still, Russia’s Gazprom says it is interested in developing the Azar oil field, and industry sources say China has been selling gasoline to Iran.