Farsi Zaban jaan:
What you may be recalling is the $20 million threshold that was set by a law called ILSA (Iran-Libya Sanctions Act) which called for US sanctions against non-US companies investing more than that amount in Iran's oil and gas sector. As long as your investment in Iran was less than $20 million, you were OK, but if you went above that amount (which in the oil and gas industry is almost impossible not to do) you were subject to US scrutiny and possible sanctions. I do not, however, know of any non-US companies that were ever actually sanctioned under ILSA.
ILSA is an old statute. A few years ago, the US enacted newer restrictions that prohibited American entities from conducting ANY business in ANY amount for ANY purpose with ANY Iranian entity, UNLESS a license to do engage in such business were granted by OFAC. The law specifically states that medical, agricultural, and humanitarian businesses may be conducted UNDER license from OFAC. Almost no other business is allowed.
These regulation has had some strange consequences. That is why TEOFL and GRE cannot test Iranian students directly in Iran - if they did, they would have to accept payment from them, and that is prohibited under the law. This may also have been behind a movement to throw out all Iranians from IEEE a few years ago, because membership of those people in the American-based IEEE may have constituted a business transaction with an Iranian citizen under the law. Normally, these problems are addressed by the American entity applying for a license to OFAC to do business with the Iranian entities it wants to deal with. Once the license is granted, they can legally do their thing.
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