Shares of British banking giant Standard Chartered fell more than 23% on the London Stock Exchange Tuesday, one day after New York regulators accused the banking group of helping Iran avoid sanctions by concealing $250 billion in transactions over nearly 10 years.

On Monday, the New York State Department of Financial Services accused the London-based bank of conspiring to hide 60,000 transactions with Iranian clients, including the Central Bank of Iran, from 2001 to 2010.

Liberum Capital analyst Cormac Leech said Tuesday that Standard Chartered could face up to $5.5 billion in costs, including fines, lost revenue and damage to the bank's staid reputation. Leech added that it's unclear whether senior managers at Standard Chartered will resign over the accusations.

Federal regulators and the U.S. Department of Justice could bring charges against Standard Chartered for violations of bank security laws and anti-money laundering regulations, among other things, according to John Alan James, an expert on corporate governance at Pace University in New York.

"I would forecast huge monetary fines, possible loss of license to do business in the United Sates, and finally, solid actions that give guilty culprits more than slaps on the hand, and jail," said James.

Meanwhile, Standard & Poor's said the bank's rating was "currently unaffected" by the investigation.

While the stock is listed in London, shares of Standard Chartered (SCBFF) that trade on U.S. over-the-counter exchanges fell more than 8% on Tuesday.

The United States and its allies have increased economic sanctions against Iran during the past few years in an effort to deter the Islamic Republic from developing its nuclear capabilities. Iran has argued that its goal is to produce energy, but U.S. officials say the Iranians are developing weapons.

Related: Washington gets tough on Iran (sometimes)

Standard Chartered allegedly falsified business and official records to mask transactions with Iranian customers that were subject to U.S. economic sanctions, the New York State Department of Financial Services said. In exchange, the global banking group reaped "hundreds of millions" of dollars in fees, according to an order issued by the New York authorities.

"Led by its most senior management, [Standard Chartered] designed and implemented an elaborate scheme by which to use its New York branch as a front for prohibited dealings with Iran – dealings that indisputably helped sustain a global threat to peace and stability," the regulators said in the document.

The regulator has ordered Standard Chartered executives to appear in New York on August 15 to answer the charges. Standard Chartered could face fines and potentially have its U.S. banking license revoked.

Standard Chartered said in a statement that it "strongly rejects the position or the portrayal of facts as set out in the order issued by the [Department of Financial Services]." The bank said it believed "well over 99.9%" of the transactions in question complied with U.S. regulations.

Related: Investors can't ignore Iran. Next Black Swan?

In its order, the New York regulator said Standard Chartered operated as "a rogue institution" by clearing illicit transactions for Iranian clients and intentionally withholding information from state and federal regulators.

Specifically, the regulators say Standard Chartered had a well-established policy of "repairing" documents in so-called U-Turn transactions, in which offshore money passes through the U.S. financial system on its way to other offshore accounts.

Under federal law, banks are obligated to ensure that such transactions do not violate U.S. sanctions. But regulators say Standard Chartered's New York branch regularly manipulated wire transfers that would have identified Iranian customers in the U-Turn transactions.

The New York branch is mainly involved in clearing U.S. dollar transactions, on average $190 billion per day, for international clients. It was first granted a license to operate in New York as a foreign bank branch in 1976.

According to the order, an official in the bank's U.S. division warned top bank managers in London in 2006 that the bank could face "serious criminal liability," according to internal emails cited in the order.

But the warning was allegedly rejected by the recipient, who responded by writing in an email: "You f—ing Americans. Who are you to tell us, the rest of the world, that we are not going to deal with Iranians."

The allegations are the latest in a string of banking scandals that have erupted this year.

Barclay's paid $453 million in June to settle charges brought by U.S. and U.K. regulators that it manipulated a key inter-bank lending rate. Deutsche Bank (DB), Royal Bank of Scotland (RBS), Credit Suisse (CS), Citigroup (C, Fortune 500), JPMorgan Chase (JPM, Fortune 500) and UBS (UBS) are among the banks that have acknowledged that they are being investigated by regulators.

The rate fixing scandal has cast a pall over the banking industry and tarnished its reputation.

"As we have seen most recently with Barclays and HSBC, it is the reputational hit and management distraction that results from these regulatory allegations that is likely to prove most costly," said Michael Symonds, a banking industry analyst at Daiwa Capital Markets.