The US Congress wants to get to the bottom of how much tax dodging is going on after a survey found that 59 of the top 100 publicly traded contractors had set up subsidiaries in so-called "tax havens".

And a new bill is being planned by Senators to halt companies moving money to low tax countries like Bermuda.

While it is unclear what the definition used by the Congressional auditors for a "tax haven" is, it appears to include Bermuda as Tyco is included in the report.

The General Accounting Office study, which was commissioned by Congress, did not determine whether the companies had in fact reduced their overall tax burden as a result of these subsidiaries.

"The question is how much tax dodging is going on," said Senator Carl Levin, one of two senators who requested the report. "This issue cries out for additional investigation," the Michigan Democrat said is a statement.

The GAO report found that some of the biggest federal contractors in the government's 2001 fiscal year had dozens of subsidiaries in countries which impose no taxes, or nominal taxes, on corporate income.

Bermuda conglomerate Tyco International Ltd. had the most subsidiaries in "tax haven" countries listed in the report ? 115 in all. Tyco had $206 million in federal contracts in its fiscal year ended September 30, 2001, said the report.

Halliburton Co., the US military's biggest contractor in Iraq, had 17 subsidiaries in "tax haven" countries.

And telecommunications provider WorldCom, now emerging from bankruptcy as MCI, had ten units in "tax havens", according to the GAO.

Altogether the 100 federal contractors had a total of 464 tax haven subsidiaries, the report said, citing information it gleaned from Securities and Exchange Commission filings.

While having these subsidiaries is not illegal, "tax haven subsidiaries are designed to duck taxes," said Senator Levin.

The Senator said he planned a bill to fight "offshore tax haven abuses and illegal tax shelters".

Tyco spokesman David Polk said the company's effective tax rate in 2003 was 42.4 percent. "When this rate is compared with similar rates for peer group companies, there is no doubt Tyco pays its share of taxes," he said in response to the report.

Halliburton, with $534 million in federal contracts in fiscal 2001, noted that it remained a US company.

"Unlike a number of our competitors who operate in the US but have moved their domicile to tax haven countries, Halliburton proudly remains a US company and has a higher effective tax rate as a result," said spokeswoman Wendy Hall.

"All of our government contracting work is done through United States companies and is fully taxable in the United States,' Hall added.

MCI spokeswoman Sudie Nolan said its subsidiaries identified in the GAO report "are legitimate operating companies which comply with current tax laws." The company had $504 million in federal contracts in fiscal 2001.