A U.S. government investigator is opening a probe into disclosures made as part of the government's rescue of American International Group Inc. when the company's trading partners were paid billions in November 2008.

Neil Barofsky, the special inspector general for the $700 billion Troubled Asset Relief Program, plans to tell a U.S. House panel Wednesday that he is investigating whether there was any "misconduct relating to the disclosure or lack thereof" surrounding the deals, in which banks who had traded with the giant...