Corporations with an interest in maintaining the current international tax code have spent millions of dollars lobbying to stop reforms, according to a study by the U.S. Public Interest Research Group.

U.S. PIRG analyzed the lobbying activities of a dozen active members of Promote America's Competitive Edge, a coalition that advocates for policies that will encourage international competitiveness for American businesses.

The 12 companies spent a total $37 million in lobbying activities and more than $6 million in campaign contributions in 2008, according to the study. The companies are: Dell, Exxon Mobil, General Mills, Hewlett-Packard, IBM, Cardinal Health, Eaton, Johnson & Johnson, Kraft Foods, Merck, Oracle and PepsiCo.

"The truth is, corporations know that contributing to campaigns and spending liberally on lobbying can help reap valuable dividends in policy decisions," Lisa Gilbert of U.S. PIRG said in a statement. "Our flawed system helps to slow the pace of reform on important issues like closing tax loopholes."

International tax code changes have been considered as a way to help pay for health care reform. One proposed change would make multinational corporations that are incorporated in tax haven countries pay taxes in the U.S. on income earned in the U.S.

Those corporations cost the U.S. $100 billion in lost tax revenue every year, according to PIRG.