U.S. Senator Orrin Hatch, the top Republican on the tax-writing Finance Committee, said billionaire investor Warren Buffett called him recently to find out what Congress might do about companies that move abroad for tax purposes.
Read MoreHow to invest in tax inversions
Lawmakers, particularly Democrats, are concerned about inversions, in which a U.S. company buys a foreign competitor and makes its home country the new tax domicile. The deals often result in lower tax rates for the inverted company.