New York's attorney general is investigating tax strategies of some of the nation's largest private equity firms, including Bain Capital, founded by Republican presidential nominee Mitt Romney, an official familiar with the probe said Sunday.

Attorney General Eric Schneiderman is examining whether the firms have abused a tax strategy to avoid paying hundreds of millions of dollars in taxes, said the official, who spoke on the condition of anonymity because of the sensitivity of the probe. The practice involves converting some fees collected for managing accounts into fund investments, resulting in a lower tax rate.

Some tax experts who spoke to The New York Times, which first reported the investigation Sunday, believed the strategy was potentially illegal, though other experts said it was commonplace and proper.

The Democratic attorney general sent subpoenas to more than a dozen firms, including Kohlberg Kravis Roberts & Company, TPG Capital, Sun Capital Partners, Apollo Global Management, Silver Lake Partners and Bain Capital, according to the official.