Inversions are a form of incorporation whereby U.S. companies (mainly multinationals) purchase a non-U.S. firm and "reincorporate" themselves based in the country of the acquisition – which invariably has lower corporate tax rates.
Most recently, Burger King has taken steps to become a Canadian corporation through its planned acquisition of Canada-based coffee-and-donut chain Tim Hortons. Some lawmakers in Congress are trying to introduce bills to discourage inversions, while others feel they should be dealt with as part of comprehensive tax reform.