Forbes | GENEVA -- UBS AG says the U.S. Internal Revenue Service has collected information on the cross-border activities of about 20 Swiss banks in the course of its amnesty program for American tax evaders.

The claim is contained in a letter sent to Swiss parliamentarians urging them to approve a treaty between Switzerland and the United States on improving cooperation on tax evasion matters.

A court decision in January forced the Swiss government to bring the treaty back to parliament to end the long-running tax dispute with the United States.

The Zurich-based bank says in the letter that "the risks for the Swiss financial center and the economy as a whole if parliament were to withhold its approval are very considerable."