The tax rates that U.S. companies would pay on an estimated $3.1 trillion in earnings they've stockpiled overseas haven't been finalized yet—and they may change depending on the final bill's revenue score, said Representative Tom Reed, a Republican member of the House Ways and Means Committee.

The House voted last month to tax companies' stockpiled offshore earnings at 14 percent for income held as cash and 7 percent for less-liquid assets. The Senate's bill this month set those rates at 14.5 percent and 7.5 percent, respectively.

As Republican leaders of the two chambers work on compromise legislation to send to Trump next week, many of the changes—including a lower rate for the highest-earning individuals and restoring or enhancing some tax deductions—would increase the bill's revenue cost.