NEW YORK (CNN/Money) - Dozens of U.S. corporations are conducting business in Iran, despite a 1980 trade sanction outlawing U.S. citizens and companies from doing business there.

Importing carpets, caviar, dried fruits and nuts is still legal, but few of these companies fall under these categories.

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According to one analyst, there are more than 30 U.S. corporations doing business in Iran through foreign subsidiaries or related companies.

"The business of subsidiaries of U.S. firms being able to maneuver around the U.S. sanctions...even though they're legal...I think that that's starting to rub people the wrong way," Roger Robinson of the Conflict Securities Advisory Group told CNN reporter Chris Huntington .

Vice President Cheney's old firm Halliburton (HAL: Research, Estimates) has an office in the Iranian capital, Tehran. A company spokeswoman told CNN that the subsidiary, Halliburton products and services, helps build drilling rigs in Iran's southern oil field.

Halliburton's main competitors in the oil field industry, Baker Hughes (BHI: Research, Estimates) and Smith International (SII: Research, Estimates), have foreign operations in Iran too.

There's also a Swiss-owned Caterpillar (CAT: Research, Estimates) dealership in Tehran and General Electric's (GE: Research, Estimates) Canadian Unit is working on a huge hydroelectric project there.

All of these companies told CNN that they are in full compliance with U.S. trade laws.

But Michael Ledeen of the American Enterprise Institute thinks that companies doing business in Iran are indirectly helping fund terrorism.

"The oil companies are a wholly owned subsidiary of the government...the government is the primary sponsor of terrorism," he said. "Plus they have separate organizations that are used to funnel oil profits and other profits into the terror network."

But the sanctions say that as long as a U.S. entity does not own or manage its foreign subsidiary in Iran, it's perfectly legal.

Halliburton's subsidiary, is registered in the Cayman Islands and headquartered in Dubai, with no Americans on staff.

"If the activities were carried out completely independently of the U.S. operations as part of an ongoing business practices of the foreign subsidiary, that would be all right," said Christopher Myers an attorney with Holland and Knight LLP.

"If they set that company up offshore with the express purpose of avoiding their obligations under US law, that could be illegal."

Enforcing trade sanctions falls under the jurisdiction of the Treasury Department's Office of Foreign Asset Control, or OFAC, and its rules on Iran are clearly posted on their website.

The OFAC Director Richard Newcomb told CNN's Huntington that his staff is ready to crack down on any U.S. citizen or company that violates the sanctions.

But the penalties for violating the sanctions tend to be modest.

Halliburton paid $15,000 in 1997 to settle a commerce department claim that it was improperly shipping oil field equipment to Iran. At the time, Cheney had just come on as the company's CEO and he was an outspoken critic of the sanctions against Iran.

When CNN inquired about the Bush administration's policy on U.S. corporate interests in Iran the Vice President's office had no comment and directed the station back to the OFAC.

But the pressure on U.S. companies with ties to Iran is building from institutional shareholders.

Pennsylvania now requires its state pension funds to monitor investments for exposure to sponsors of terrorism.

New York City Comptroller William Thompson, who oversees the pension funds for New York City's police force and firefighters, has forced Halliburton and Conoco-Philips to review their business dealings in Iran and Syria.

"Those United States-based companies have to be really concerned and if I were in their shoes I'd take a fast look at the work that I'm doing in these nations and in the end, most of them will make the claim that its not a large piece of their business," said Thompson. "

"Well, since it isn't, get out and get out now."

But he couldn't persuade General Electric to leave.

GE's proxy stated that a review of its business in Iran would be unnecessary because, "We are compliant with U.S. law and regulations which recognize that foreign subsidiaries of U.S. companies can and will do business in Iran."

For decades U.S. economic interests in Iran have been at odds with national security policy, particularly when oil is involved and for now U.S. corporations have all the legal insulation they need to carry on business as usual in Iran.