The Australian Tax Office (ATO) has raided the properties of 20 wealthy Australians over claims they have used bank accounts in Liechtenstein to avoid paying tax.

Tax Commissioner Michael D'Ascenzo says the investigation involves amounts ranging from $200,000 to millions of dollars and is part of an international probe involving nine countries.

Mr D'Ascenzo says the ATO has already conducted raids and issued notices to produce information to the 20 Australians who have suspected links to Liechtenstein accounts.

He says the inquiries are continuing and the final tax bill is still unclear.

The US Internal Revenue Service said it was investigating more than 100 American taxpayers over bank accounts held in Liechtenstein.

"Combating off-shore tax avoidance and evasion are high priorities," the IRS said in a statement.

"We are determined to protect the US tax system from abuse and ensure that taxpayers pay what they owe ... It should be clear from recent events that there is no safe hiding place for the proceeds of tax avoidance and evasion."

Italy and France were quick to follow suit, saying that they had found their nationals on a list of names with accounts in Liechtenstein being circulated by the tax authorities.

Spain also announced that it was looking at information regarding several citizens included on a list of people with bank accounts in Liechtenstein.

'Immoral behaviour'

The Australian Council of Trade Unions (ACTU) leader says wage earners will be outraged by claims that wealthy Australians have been using secret overseas bank accounts to avoid paying millions of dollars in tax.

ACTU President Sharan Burrow says working Australians would be appalled by the tax avoidance schemes.

"Well this is just immoral, and I don't think any working Australian can sit back and understand why it is that people who are so wealthy, that they couldn't spend the money the earn anyway, would go to the extent of avoiding contributing to a decent Australia," she said.

The ATO has urged other taxpayers who might be involved to come clean, saying that indemnity from criminal prosecution might be possible if they provide information about the promoters of tax avoidance schemes.

- ABC/AFP