The report contains the results of a two-year Senate investigation and comes a day before the heavily-anticipated questioning of Credit Suisse chief Brady Dougan and other top bank officials before the panel.

Bank figures suggest there were "nearly 19,000 US customers with hidden Swiss assets totaling nearly $5 billion" as of 2006, the Senate report said.

That figure represents some 85 percent of the bank's more than 22,000 US customers in 2006 with Swiss accounts whose assets, at their highest, exceeded $13.5 billion, the report said.

Among the bank's cloak-and-dagger practices, Swiss bankers were sent to the United States to secretly find clients, leaving no paper trail, at events sponsored by the bank — such as at golf tournaments in Florida.

The bank also helped its clients find "intermediaries" who could help them create offshore shell companies to hide the money trail from the Internal Revenue Service.

"One former customer described how, on one occasion, a Credit Suisse banker traveled to the United States to meet with the customer at the Mandarin Oriental Hotel and, over breakfast, handed the customer the bank statements hidden in a Sports Illustrated magazine," wrote the investigators.

Third-party companies were also engaged by the bank to provide credit cards permitting clients to secretly use their hidden funds.

"The battle against tax havens using secrecy laws to facilitate US tax evasion has bogged down, causing a huge loss to our treasury" said Senator Carl Levin, chairman of the Senate subcommittee that led the investigation.

By 2008, the report says, there were more than 1,800 Credit Suisse bankers employed to manage US client accounts, many of which were never declared to the IRS, and whose transactions were structured to avoid US tax reporting requirements.

From 2008 to 2011, after the break of a tax evasion scandal at fellow Swiss bank UBS, Credit Suisse starting putting an end to its evasive practices, asking clients to close their accounts or declare them.

"The Department of Justice has failed to use the US legal tools that won the UBS case," Levin said.

"It's time to ramp up the collection of taxes due from tax evaders on the billions of dollars hidden offshore," he added.

In total, by the end of 2013, the number of Swiss accounts held by US clients at Credit Suisse fell by 85 percent, or the 19,000 clients believed to have had hidden assets, the report said.