Already facing criticism for its plans to become an Irish company to avoid U.S. taxes, Medtronic, the Minnesota-based medical device maker, disclosed this week that it pays very little in taxes in the foreign countries where it claims to have profits.

The company, which made waves recently with its ongoing effort to “invert” its corporate structure so that it becomes (at least on paper) an Irish corporation, doesn’t appear to be facing major obstacles to this effort.

But it’s not taking any chances. Whether the corporate inversion deal ultimately goes through or not, the company continues to aggressively shift profits and cash offshore to avoid U.S. tax. In Medtronic’s just-released annual financial report, the fine print reveals that the company’s total “permanently reinvested” foreign profits—that is, income they have said they have no intention of bringing back to the U.S.—rose from $18.1 to $20.5 billion in the past year. And the total amount of cash and cash equivalents that the company holds abroad rose abruptly from $10.9 to $13.9 billion in just one year.

The tax implications of Medtronic’s offshore cash—to say nothing of the $2 trillion in permanently reinvested earnings held by Fortune 500 companies overall—could be enormous. The company is supposed to pay the 35 percent U.S. tax rate (minus any taxes already paid to foreign nations) on these earnings when they are “repatriated” to the U.S. In its financial statements, the company declined to disclose whether it has paid any tax at all on its permanently reinvested foreign earnings. It hid behind an accounting standards loophole that allows companies to avoid disclosure if calculating the U.S. tax would be “impracticable.” Only 58 of the 301 Fortune 500 companies that have offshore profits estimated the U.S. tax on those earnings in their most recent annual reports.

But in response to a reporter’s inquiry this week, Medtronic admitted that the U.S. tax due on those foreign profits would be 25 to 30 percent.  We’re willing to bet that just like Medtronic the other profit-shifting U.S. multinational companies know exactly how much it will cost to repatriate those earnings, but don’t want to let the public know of their tax-dodging ways.

Medtronic’s 25 to 30 percent estimated U.S. tax liability tells us that a substantial amount of the so-called offshore profits are accumulating tax-free. The company’s 37 subsidiaries located in known tax havens adds to the suspicion: the company has five subsidiaries in the Cayman Islands alone. Unless the company has identified a huge untapped medical-device market in the Caymans, it’s probable that the main reason why Medtronic owns these subsidiaries is to shelter their cash tax-free.

If, as seems likely, Medtronic’s inversion proceeds as planned, its “foreign” earnings in these tax havens may forever escape tax. But the company potentially stands to benefit from shifting profits, on paper, into tax haven countries even if they are not allowed to renounce their Minnesota citizenship.

Some in Congress continue to float the idea of a repatriation “tax holiday” that would allow companies like Medtronic to pay a sharply reduced tax rate on their tax haven profits upon repatriation.

So Medtronic’s ongoing off shoring effort is a profitable tax dodge no matter what happens to their inversion effort. It’s time for Congress to put a stop to it.