Multinational corporations could end up shifting even more of their income to low-tax countries under some tax reform proposals, according to a new study.

The study, by Scott D. Dyreng of Duke University and Kevin S. Markle of the University of Iowa, examined the effects of financial constraints on income shifting by 2,058 U.S.-based multinationals from 1998 to 2011 if the U.S. were using a territorial taxation system, as has been proposed by some tax reform proponents.

Under a territorial tax system, companies are only taxed on their domestic income, whereas under the current worldwide system of taxation they are supposed to be taxed on both domestic and foreign profits as long as they are not subject to double taxation. In practice many multinationals are able to defer taxation of their foreign profits until the money is repatriated to the U.S.

The researchers estimate that, if a territorial system of taxation had been in effect over the time period the examined instead of the current tax system, the financially constrained companies in the sample would have shifted approximately $80 billion more of their income out of the country, translating to about 8 percent more than the amount shifted by the companies in the sample.

Assuming the financially constrained companies paid the statutory corporate tax rate of 35 percent on the income they did not shift to another country (which is more than the effective rate actually paid by many companies), the loss to the U.S. Treasury would have totaled $28 billion during the 14-year period.

The study suggests a territorial system could indeed lead to more income shifting abroad by hundreds of companies that now are financially constrained from doing exactly that. However, at a time when federal budgets are in the trillions of dollars, the loss in tax revenue is likely to be modest in comparison. The researchers cautioned that their study does not include all U.S. multinational companies, but it does comprise a large sample of them.

The study appears in in the November issue of the American Accounting Association journal The Accounting Review.

The chances for tax reform after the election depend on the outcome, but multinatioonal companies are already trying to influence what happens. A new analysis by Bloomberg Government found that 125 U.S.-based Fortune 500 multinational corporations with offshore holdings spent a total of $230 million lobbying Congress on issues such as taxation during the first six months of this year.