Apple CEO Tim Cook is  appearing before the Senate Permanent Subcommittee on Investigations  today to answer charges that his company has avoided paying billions of dollars in taxes through the use of overseas tax shelters and loopholes in the corporate tax code. An investigation by the subcommittee found that Apple has shifted tens of billions of dollars of two subsidiaries in Ireland, while claiming that neither subsidiary is a tax resident of any country.

Apple (like many giant, multinational corporations) has been avoiding paying the taxes they owe to the country by setting up foreign “subsidiaries” in tax-haven countries and moving jobs and profit centers out of the country. They have accumulated billions upon billions of dollars in these tax havens. Now they want a special tax break to reward them for doing that.

Current laws in the United States allow corporations to use offshore havens to avoid paying their taxes and, if it's up to many in Washington, the problem will only grow larger, particularly if the so-called "territorial" tax system is passed. The details of the use of such tax havens were discussed in a conference call with Campaign for America's Future , Americans for Tax Fairness  and Citizens for Tax Justice .

Over the past 40 years, some of the nation’s biggest and most profitable companies have not only moved America's jobs and manufacturing overseas, but by taking advantage of a U.S. tax code that encourages companies to shift their income overseas, they have cut the taxes they owe by more than half. The result, writes Jia Lynn Yang in The Washington Post ,

is lower revenue here that could pay for infrastructure, education and other services that support domestic growth—and that make life easier for U.S. firms.

A new report from the U.S.  Public Interest Research Group  (PIRG) reveals that state governments lost $39.8 billion in revenues because corporations and wealthy individuals are using offshore tax havens to avoid paying their statutory tax rates. We've seen the devastating effects that offshoring jobs have had on America's workers, and offshoring has long been talked about in terms of lost federal revenue, where $150 billion a year goes unpaid, but little focus has been given to state losses from the practice.

A Senate bill introduced this week would prevent some of the worst tax-dodging tactics by corporations that use offshore tax havens and also raise about $155 billion in additional revenue over 10 years.