Alliantgroup LP is a politically connected advisory firm that helps companies apply for lucrative tax credits. Clients have ranged from Oscar de la Renta to an Arkansas candle maker.

The firm also helps companies sidestep taxes, two former employees alleged in July 2009. In a 32-page submission filed with the Internal Revenue Service, along with internal e-mails and documents, they claimed Alliantgroup's clients could owe the U.S. Treasury as much as $712.5 million in refunds over wrongly claimed tax credits. The whistleblowers stood to make more than $210 million, under a law that offers informers as much as 30 percent of what the government recovers from their tips.

Twenty-one months later, the IRS rejected the claim, without its auditors ever talking to the whistleblowers and even after a request by some agents to convene a grand jury, internal agency documents show.