LONDON -- Standard Chartered (LSE: STAN.L) has now joined the ranks of Lloyds Banking, Barclays, and HSBC among international banks falling foul of U.S. sanctions on Iran and terrorist groups. Their indiscretions have cost the other three banks 863 million pounds collectively (though HSBC's fines could go higher), and an even weightier fine could be headed Standard Chartered's way.

Importantly, the New York Department of Financial Services -- an organization not even a year old -- and its superintendent, Benjamin Lawsky, are flexing their regulatory muscle and threatening to strip Standard Chartered of its U.S. banking license.

While not particularly damaging on the surface -- almost 90% of Standard Chartered's profits come from Asia and Africa -- the loss of a U.S. banking license would have implications for the bank's global operations. Without a U.S. banking license, the ability to process U.S. dollar-denominated trade financing becomes significantly more difficult and could result in a material loss of business.

However, Standard Chartered isn't taking the allegations of hiding 60,000 transactions with Iranian clients lightly. The bank has issued a statement saying it "strongly rejects the position and portrayal of facts made by the New York Department of Financial Services" and feels that the charges as presented do not offer "a full and accurate picture of the facts."

The bank claims to have been working with U.S. authorities for more than two years as part of an internal review of its compliance with U.S. sanctions on Iran and other countries.

Regardless of whose story is accurate, these allegations taint yet another U.K. bank and surround Standard Chartered with uncertainty that quickly erased last week's solid results and sent shares plummeting 24% during today's trading.

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Nate does not own any shares discussed above. The Motley Fool owns shares of Standard Chartered. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.