Three members of the United States House of Representatives have accused Switzerland's largest bank, UBS, of laundering money for the Cuban government.
They are calling for an investigation into transactions worth $3.9 billion (SFr4.9 billion) alleged to have been made between 1996 and 2003.
Ileana Ros-Lehtinen, a Cuban-born Republican and congressional representative for the state of Florida, wants to track the money.
She claims the Swiss bank carried out 1,900 transactions with the government of Cuban leader Fidel Castro over the seven-year period.
"We want to know the exact source of the money," said Alex Cruz, a spokesman for Ros-Lehtinen.
"We are convinced that UBS employees laundered money."
UBS spokesman Christoph Meier said he had not been informed of any new investigation of the bank and rejected all accusations of money laundering.
Old for new
Ros-Lehtinen and her colleagues accuse UBS of buying old dollars from the Castro government and then crediting an account with new US banknotes.
The transactions would have been in violation of a US economic and financial embargo against Cuba, which has been in place since 1962.
At the time, UBS was one of a number of foreign banks contracted by the US Federal Reserve to exchange new dollar bills for worn-out notes being taken out of circulation.
But the contract specifically stated that the banks were not allowed to do business with countries under US sanctions.
Ros-Lehtinen has also cast doubt on the Cuban government's explanation that the $3.9 billion flowed from tourism.
"Given the quantity we're dealing with, it is doubtful that the funds derived from tourism,” she said in a July 12 letter to Federal Reserve Chairman Alan Greenspan.
“Rather, [the money] could have stemmed from one of Castro's nefarious activities, such as drug trafficking.”
Ros-Lehtinen said the matter had been discussed during a meeting with UBS representatives on Thursday, but added that many questions remained unanswered.
Christine Whalton, spokeswoman for UBS in New York, declined to give any details about the meeting.
In the House of Representatives, Ros-Lehtinen chairs the International Relations subcommittee on the Middle East and Central Asia.
She started investigating UBS two months ago, after the Federal Reserve fined the bank $100 million for violating US embargoes against Iran, Libya, Cuba and the former Yugoslavia.
UBS had agreed not to carry out dollar transactions with countries under embargo.
But an internal investigation found that dollars had been traded and that UBS employees submitted false reports to the US authorities in a bid to conceal the transactions.
Several members of the bank's staff have since been dismissed and others sanctioned.
The Federal Reserve cancelled its contract with UBS last year.
swissinfo, Elizabeth Meen
UBS is the world’s sixth-largest bank and the leading global asset manager.
It was formed in 1998 following the merger of the Union Bank of Switzerland and the Swiss Bank Corporation.
It employs a staff of 65,630.
In May it reported a record first-quarter net profit of SFr2.42 billion ($1.86 billion).
Three members of the US Congress have accused Switzerland's biggest bank of “laundering” Cuban money.
They are demanding an investigation into $3.9 billion allegedly deposited in a single UBS bank account between 1996 and 2003.
They claim UBS bought old US dollars, then credited the account with new dollars, violating a US embargo.