Certain Swiss banks are blocking clients from gaining full access to offshore accounts in connection with tax treaties being negotiated between Switzerland and Germany, the UK and the US, Bloomberg has quoted the Swiss banking ombudsman as saying.

“This is a new type of complaint we’re getting this year," Hanspeter Haeni said, adding that he’s not allowed to disclose the names of the banks. “I’m afraid there will probably be more such cases.”

The report did not elaborate on which specific banks were blocking client access. A number of banks, such as UBS, Julius Baer and Wegelin, no longer provide offshore banking services to clients in the US, for example.

Total complaints in 2011 from foreign clients about treatment by Swiss banks have already overtaken the 39 made for the whole of 2010. The 44 complaints received by the ombudsman’s office this year come mostly from customers with US citizenship or a green card and from Germany, Haeni reportedly said.

Switzerland is in talks with Germany, the UK and the US about resolving the issue of untaxed assets held in Swiss bank accounts. The countries are negotiating about proposed withholding taxes on interest, dividends, capital gains and investment income earned by clients with offshore bank accounts as well as levying a tax for past non-disclosure.

The number of complaints to the ombudsman has been rising since the Swiss authorities permitted UBS in 2009 to disclose data on more than 4,500 US clients suspected of tax evasion to the Internal Revenue Service. That agreement was seen at the time as a serious breach of Switzerland’s historic bank secrecy laws.

The stakes for Switzerland in protecting its banking industry are large: finance accounts for about 12 per cent of the Alpine state’s gross domestic product.