The official spoke on the condition of anonymity because of the sensitivity of the probe. It is examining whether the firms used a tax strategy to avoid paying hundreds of millions of dollars in taxes. The practice involved converting some fees collected for managing accounts into fund investments, resulting in a lower tax rate.
The New York Times first reported the investigation of more than a dozen firms. Tax experts tell the Times they have differing views about the strategy's legality.
Though Romney collects benefits as a Bain retired partner, the inquiry isn't focused on the time he ran Bain.
(Copyright 2012 by The Associated Press. All Rights Reserved.)