Treasury Secretary Jack Lew on Thursday announced new administrative efforts to prevent U.S. corporations from moving their headquarters out of the country to save on taxes, and promised more to come.

Lew announced a notice to issue five new items of guidance meant to limit so-called corporate "inversions," three meant to prevent companies from moving their headquarters outside the U.S. and two to prevent companies that have undergone inversions from transferring taxable income out of the country.

"These actions futher reduce the benefits of an inversion, and make these transactions even more difficult to achieve," Lew said on a teleconference with reporters.

He called the new rules "an important step, but not the end of our work."

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