According to a Swiss wire report, the IRS has upped the ante in its fight to gather thousands of names of alleged tax-dodging American UBS clients: By sending IRS agents to tail the firm’s bankers and financial advisors as they visit clients.

It’s the latest in the ongoing cross-border dispute between U.S. authorities and the Swiss asset manager. The tax dispute has been making headlines across the world and has embarrassed the firm and its employees, particularly its bankers and financial advisors who deal with wealthy clients.

But according to the story posted yesterday in the Swiss weekly, Sonntags-Zeitung, a possible compromise could end up revealing 10,000 of the American, UBS-client names the IRS is seeking.

The IRS estimates that tens of thousands of American clients have hidden $20 billion in UBS offshore accounts, evading $300 million in taxes a year. UBS, meanwhile, made $200m a year in profits from its offshore banking business. The former head of UBS Global Wealth Management International, Raoul Weil, is still a fugitive from US justice, allegedly hiding in Switzerland, away from the criminal charges laid personally against him in November of last year.

The Swiss have so far refused to reveal the names of approximately 52,000 American clients the IRS alleges have evaded U.S. taxes with the help of UBS advisors. The Swiss say doing so would violate Swiss banking laws.