The arrangement would allow German tax authorities to make requests dating back to 2011 about people they suspect of moving their money from Switzerland to another country before the agreement to tackle German tax dodgers hiding money in Switzerland takes effect, Focus weekly magazine said.

The Swiss parliament is due to pass a law to allow this in the coming months, the magazine said, adding it would not require And change or renegotiation to the agreement which Berne struck with Berlin in April to levy taxes on German assets in Swiss accounts.

That would make the deal more appealing to the Social Democrats (SPD), Germany's main opposition party, who have said they would veto it in its current form. The German government needs SPD backing for it in the upper house.

One of the SPD's criticisms has been that, as it stands, the agreement would allow people to evade taxes by taking their money out of Switzerland before the deal takes effect.

Senior SPD member Joachim Poss suggested to Berliner Zeitung newspaper on Saturday that Germany and the European Union would have to consider limiting or even banning Swiss banks from doing business in Germany if Switzerland did not cooperate.

"Tax havens like Switzerland disturb the order in the whole of Europe," he was quoted as saying.

Chancellor Angela Merkel's government says the deal would enable Berlin to net huge sums if and when it takes effect. Germans hold an estimated 150 billion euros ($184.45 billion) in Swiss accounts.

However, the agreement, due to come into force next year, has been thrown into some doubt because German officials have angered the Swiss by purchasing several CDs containing Germans' bank details from whistleblowers as part of a drive to identify tax evaders.

About 62 percent of Germans are in favor of their tax authorities buying more Swiss CDs containing data on evaders according to a survey by GfK market research group due to be published in Welt am Sonntag newspaper on Sunday.

German Foreign Minister Guido Westerwelle criticized such purchases in Die Welt newspaper's Saturday edition: "It is unsavory and questionable to buy stolen goods. We need to put an end to these business methods," he was quoted as saying.

Westerwelle also called on Germany's federal states to make the purchase of tax CDs unnecessary by ratifying the tax agreement with Switzerland as quickly as possible.

The German chairman of Swiss bank UBS (UBSN.VX) said in an interview published on Sunday he had no evidence the bank data leaked from his company.

Switzerland's State Secretariat for International Financial Matters, which is responsible for questions related to the Swiss-German tax deal, was not immediately available for comment. ($1 = 0.8132 euros)

(Reporting by Michelle Martin; Editing by Alison Williams and Andrew Heavens)

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