In 2008, the U.S. placed a ban on financial institutions doing business with Iran or Iranian firms. Prior to the all-out ban, business with Iranian firms was allowed, but only if it could be proven that the financial dealings "were not improper." Abiding by both these rules has been a prerequisite for gaining and/or maintaining a financial license to operate in the U.S.
Enter Standard Chartered, a large British bank that stands accused of "ignoring the 2001-2008 regulations and trying to hide some $250 billion in transactions with Iranian companies."
As of right now, the New York State Department of Financial Services (DFS) stands ready to revoke Standard Chartered's license for operations in the U.S., and is asking the bank to provide justification for why it's license shouldn't be taken. Making matters worse, the DFS has also alleged that Standard Chartered is a "rogue institution," and is demanding bank representatives appear before the DFS to answer questions on August 15.
It was just last month that the U.S. Senate accused HSBC, another British bank, of violating the 2001-2008 rules governing financial dealings with Iran.