According to Swiss daily TagesAnzeiger, state secretary for international affairs Michael Ambuehl will transmit by Tuesday evening information on the number of accounts and the total sum held by US citizens in Switzerland.
The Swiss Financial Market Supervisory Authority surveyed a number of Swiss banks and determined that between $20 billion to $30 billion dollars (€14.2-21.3
billion) was held by "tens of thousands" of US customers, the newspaper said.
According to the weekly SonntagsZeitung, the United States has asked for detailed information on US nationals who have hidden their money in Switzerland, basing its report on a letter from the US deputy attorney general James Cole dated August 31, addressed to Swiss authorities.
The letter mentioned Switzerland's second-biggest bank, Credit Suisse, as well as about another 10 banks, notably Julius Baer, Wegelin, and the cantonal banks of Zurich and Basel, the Sunday paper alleged.
US authorities want all the data concerning private customers and US foundations which have deposited at least $50,000 (around €35,000) in Switzerland between the period of 2002 and July 2010, it said.
Swiss finance minister Eveline Widmer-Schlumpf said on Monday on Swiss television that she disagreed with the ultimatum.
"This is not how to deal with other states," she said.
"We have suggested to the Americans how to solve (...) the problem," she said, explaining that a solution would have to be based on existing fiscal agreements between the US and Switzerland, or on recent agreements with Germany and the United Kingdom.
This latest request is not the first by US officials. Switzerland's biggest bank UBS was forced to disclose the names of 4,450 US clients for whom it had offered to conceal funds from the eyes of the US tax inspectors.
Widmer-Schlumpf added the use of emergency laws, as was the case for the UBS affaire, was excluded.