Medtronic Inc., famous for heart devices, also has a less-well-known distinction: It's one of the 30 U.S. corporations with the most money parked offshore.

The Fridley-based medical device maker holds $20.5 billion overseas, just one notch below Wal-Mart Stores Inc. with $21.4 billion, according to a report released Thursday.

Medtronic is one of more than a dozen Minnesota corporations in the joint report by Citizens for Tax Justice and U.S. Public Interest Research Group, which are calling for an end to the abuse of offshore tax havens.

The study uses 2013 data to examine the number of subsidiaries Fortune 500 companies have in countries regarded as tax havens, such as Bermuda and the Cayman Islands, and the amount of money they report holding offshore in general.

Medtronic, for instance, has 37 subsidiaries in so-called tax haven countries.

The authors say they can't determine exactly how much of the money companies keep offshore is in tax-haven countries vs. other overseas locations where the companies have operations. However, there's evidence that a significant portion comes from the widespread use of accounting techniques to book profits outside the United States to avoid paying the 35 percent U.S. corporate income tax on it.

The authors point to a Congressional Research Service study showing that in 2008 U.S. multinationals collectively reported 43 percent of their foreign earnings in five small tax-haven countries, countries that accounted for just 4 percent of their foreign workforce and 7 percent of their foreign investment.

Such practices reduce federal revenue by $90 billion a year, the report said.

"Congress has left loopholes in our tax code that allow this tax avoidance, which forces ordinary Americans to make up the difference," the report said.

The Tax Foundation, a tax think tank in Washington, issued a statement Thursday calling the report misleading. The foundation criticized the study for using an overly broad description of tax haven to include such countries as Ireland and Hong Kong, for instance, and for using only Fortune 500 companies.

"According to IRS data, over 60 percent of foreign corporate income is reported in Europe and Asia, where this income faces effective tax rates of 31 percent and 26 percent, respectively," the Tax Foundation said.

Asked on CNBC Thursday whether having so much cash reside overseas creates limits on Medtronic's investments in the United States, CEO Omar Ishrak said it does.

"If we had access to that cash in a completely free fashion, then there are investments in the U.S. that we would make," he said. "Right now we would still make [the investment] if it is compelling enough, but obviously the equation is slightly different."

The study also found that 3M Co. has 12 subsidiaries in offshore tax havens and reports having more than $9.7 billion booked offshore.

General Mills Inc. has 55 subsidiaries in offshore tax havens, including seven in Bermuda, three in Luxembourg and two in Mauritius. It reports more than $2.7 billion booked offshore.

And the report said Ecolab Inc. is one of the top 20 companies ranked by number of subsidiaries in tax havens. It has 91, although 41 are in the Netherlands, where Ecolab has operations via its 2012 acquisition of Nalco.

Companies are supposed to disclose in their public filings how much they would pay in taxes if offshore money were in the United States, but only about 55 Fortune 500s did so, the report said, because companies don't have to report it if it's "not practicable." Together, those 55 companies would owe more than $147.5 billion in extra federal taxes.

Staff writer Evan Ramstad contributed to this report.

Jennifer Bjorhus • 612-673-4683