The European Union's tax chief, Frits Bolkestein, has attacked Switzerland for refusing to go along with EU plans to crack down on tax evasion.
He also accused some EU members of trying to scupper the EU's plan, which demands the scrapping of banking secrecy.
Bolkestein's comments came ahead of a meeting of EU finance ministers in Luxembourg on Tuesday, where the issue of bilateral negotiations with Switzerland was expected to be on the agenda.
Writing in Monday's "Financial Times", Bolkestein said he found it "difficult to believe that the Swiss government is hesitating to help its EU neighbours to uphold their own laws, including fiscal ones".
"We are asking the most normal thing in the world from the Swiss authorities," he added, "namely to help to ensure that EU citizens pay their taxes... I cannot stand cheats or free-riders. Nor can I stand those who make money from the often-lucrative custom of tax cheats."
Bolkestein also had harsh words for some EU members, which he accused of trying to derail the plan.
In a veiled reference to Britain, Belgium, Luxembourg and Austria - Bolkestein said: "Many within the EU... have grown rich by attracting the custom of tax evaders and are not in a hurry to lose that custom.
"Indeed, some of those calling for the strongest possible measures to fight the evasion of savings tax are doing so in the hope that by setting the standards unrealistically high, they will wreck the whole enterprise."
The EU is forging ahead with plans to impose a system of automatic exchange of information on foreign bank accounts held by its citizens.
But the EU directive, which is due to come into force by the end of the year, is dependent on the cooperation of a number of key non-EU countries, including Switzerland and the United States.
Belgium, Luxembourg and Austria have made their cooperation with the EU conditional on the participation of other third party states.
"These three EU members would much rather hang on to their financial privacy and have a withholding tax," said James Nason, spokesman for the Swiss Bankers Association.
"But they have outsourced the battle to defend financial privacy to [Switzerland] and every now and then they're peeping through their fingers to see how the battle is going."
Villiger has defended his country's reluctance to share banking information with the EU, arguing that such a move would compromise existing legislation governing banking secrecy.
A compromise deal tabled by the Swiss to levy a withholding tax on bank accounts held by EU residents has failed to win favour in Brussels.
The main opposition is said to come from Britain, which has long resisted any EU withholding tax on savings over fears that it would damage the City of London's tax-free Eurobond market.
Villiger under pressure
At Tuesday's meeting, Villiger is likely to face renewed pressure from EU finance ministers - including the threat of possible sanctions against Switzerland - if he continues to reject calls to share information with Brussels.
Responding to Bolkestein's comments in the "Financial Times", Villiger's spokesman, Daniel Eckmann, said it was unfair of the EU commissioner to "reproach Switzerland for not making any progress... particularly if you compare Switzerland's attitude with that of other third party countries".
On Monday, divisions emerged in the EU over the issue, when Luxembourg and Germany clashed publicly on Brussels' attitude towards Switzerland.
Addressing a conference in Luxembourg, the prime minister, Jean-Claude Juncker, slammed the EU's heavy-handed approach.
"The way in which some of my colleagues are trying to negotiate with the Swiss is not acceptable. They are treating Switzerland like an alpine Iraq. I won't stand for it."
But Germany's deputy finance minister, Caio Koch-Weser, speaking at the same meeting, said Switzerland's banks and businesses were aware that banking secrecy was not viable in the long-term.
Ultimately, the issue may be decided by Washington. Brussels is also trying to persuade the US to cooperate with its directive, but so far Washington has remained silent on the issue, at least publicly.
Koch-Weser said he had "no doubt" the US was prepared to exchange information with the EU, but Juncker said he had a different impression.
For his part, Bolkestein is less confident that the EU will prevail.
"Opponents of the EU's savings tax initiative may yet succeed," he writes.
"If the enemies of this initiative do manage to wreck it, it will become clear who are the friends of the tax cheats and who are not."
The EU has called on Switzerland to participate in plans to share information on Swiss bank accounts held by EU citizens.
The Swiss are refusing to cooperate because doing so would contravene banking secrecy.
Bern has instead proposed a withholding tax on EU citizens' bank accounts which it would pass on to Brussels.