The Standard Chartered share price has dropped sharply as investors react to US charges that the bank was involved in laundering money for Iran.
Shares were down nearly 20 per cent at 1,187 pence at one point in early trading on Tuesday on the London Stock Exchange.
In Hong Kong, they were down 16.6 per cent near the end of the session.
New York State Department of Financial Services alleged on Monday that Standard Chartered schemed with the Iranian government to launder $US250 billion ($A237.50 billion) from 2001 to 2007, leaving the United States' financial system "vulnerable to terrorists".
Standard Chartered said it "strongly rejects" the allegations.
In a statement, the bank said "well over 99.9 per cent" of the questioned transactions with Iran complied with all regulations, and the exceptions amounted to $US14 million.
The New York regulator ordered Standard Chartered representatives to appear in New York City on August 15 "to explain these apparent violations of law" and to demonstrate why its licence to operate in the State of New York "should not be revoked".
Gary Greenwood, analyst at Shore Capital in London, said the possible revocation of the New York licence was of far greater concern than any potential fine, which could run into hundreds of millions of dollars.
Standard Chartered's US operation facilitates trade for customers that have operations in both the United States and emerging markets.
"Indeed, this is an area of the business that has been highlighted by management for growth," Greenwood said.
"A loss of its US banking licence would not only jeopardise part of this profit stream, but the associated reputational damage could also have a severely damaging impact to its operations within emerging markets."
The New York agency alleged that Standard Chartered conspired with Iranian clients to route nearly 60,000 different US dollar payments through Standard Chartered's New York branch "after first stripping information from wire transfer messages used to identify sanctioned countries, individuals and entities".
The New York regulators called the bank a rogue institution and quoted one of its executives as saying: "You (expletive) Americans. Who are you to tell us, the rest of the world, that we're not going to deal with Iranians."
The order also identifies an October 2006 "panicked message" from a London group executive director who worried the transactions could lead to "very serious or even catastrophic reputational damage to the group".
If proven, the scheme would violate state money-laundering laws.
The order also accuses the bank of falsifying business records, obstructing governmental administration, failing to report misconduct to the state quickly, evading federal sanctions and other illegal acts.
Between 2004 and 2007, about half the period covered by the order, the department claims Standard Chartered hid from and lied about its Iranian transactions to the Federal Reserve Bank of New York.
Before 2008, banks were allowed to transact some business with Iran, but only with full reporting and disclosure, the order states.
In 2008, the US Treasury Department stopped those transactions because it suspected they helped pay for Iran to develop nuclear weapons and finance terror groups including Hamas and Hezbollah.
The order states the bank has to provide information and answer questions to determine if any of the funding aided the groups or an Iranian nuclear program.
Last week, Standard Chartered's chief executive, Peter Sands, boasted that the bank has racked up a 10-year string of record first-half profits "amidst all the turbulence in the global economy and the apparently never-ending turmoil in the world of banking".
"It may seem boring in contrast to what is going on elsewhere, but we see some virtue in being boring," Sands added.