The Organisation for Economic Cooperation and Development has singled out Switzerland in a new report for having "harmful tax practices"
The Swiss have been under pressure to scrap tax rules that make the country attractive to foreign holding companies and so-called "PO box firms".
Daniel Eckmann, a spokesman for the Swiss finance ministry, on Friday confirmed the blacklisting which is contained in a preliminary report by the OECD's "Forum on Harmful Tax Practices".
Switzerland - which abstained from the forum when it was created in 1998 - is the only OECD country to be named by the body.
International firms including Wal-Mart, Philip Morris, Gillette and Procter & Gamble base their headquarters in Switzerland - drawn to the country's low corporate tax rates and attractive financial conditions.
Although the move does not create any legal obligations on the Swiss, it could tarnish the country's international image and undermine its attractiveness to foreign firms.
"This is not acceptable," Eckmann, told swissinfo. He added that Switzerland would defend its interests at the next meeting of the OECD's tax committee - which will adjudicate the forum's report - in July.
The OECD threat dates back to 1998 when the organisation launched the forum as part of its global fight against tax evasion.
In June 2000, Switzerland was listed among dozens of developed countries as having "potentially" harmful practices. Since then, governments around the world have been modifying their taxation systems.
An OECD spokesman said that since then, Switzerland had not changed its tax practices.
Eckmann earlier this month hinted that the forum was unfairly targeting Switzerland, while well-known tax havens around the world may escape mention.
"We have big difficulties understanding how after five years of discussions about what should be considered a harmful tax practice, the forum comes up with a report that considers Switzerland the only country in the whole OECD with harmful aspects in its tax legislation," he said.
A delegation of Swiss tax officials is currently negotiating with the OECD in an attempt to avert a listing.
The government is also considering whether to use its OECD veto to block the sanction, although Eckmann said Bern was confident of avoiding such a move.
"We will put forward our best arguments to the OECD to show them that this report is not correct," Eckmann said.
"We won't make any concessions in this field because we are convinced that our system is OK," he added.
Although Eckmann declined to criticise specific countries, he said the potential blacklisting was motivated by governments eager to break Switzerland's attractiveness to global firms.
"Competition among countries to [host] these companies is fierce, and it's only natural that every country looks to have favourable frame-work conditions," he said.
"This report from the OECD has to be seen in this light."
PO box firms
However, critics question Switzerland’s tolerance of holding companies that do little immediate business within the country.
The “NZZ am Sonntag” newspaper recently said some 3,500 companies were registered as domiciled bodies in the canton of Zug alone - all of them no more than post offices.
Despite criticism of such “shell-companies”, Eckmann said the OECD row was about winning the attention of big firms seeking stable countries in which to base their global operations.
For many companies, Switzerland remains an ideal location for top-tier managers, thanks to its political stability and high standard of living - as well as the financial incentives.
swissinfo, Jacob Greber in Zurich
An OECD body has named Switzerland as a country that has "harmful tax practices".
The Swiss Finance Ministry says the move is "unacceptable".
The listing could damage Switzerland's reputation.
In 2000, the OECD said Switzerland's treatment of "holding companies" was potentially harmful.
Wal-Mart, Philip Morris, Gillette and Procter & Gamble are just some of the international firms with headquarters in Switzerland.