Adam Levine, the former PR chief of TPG Capital who was sued by the private equity firm in January, has countered with a whistleblower suit against TPG.

Levine alleges the firm threatened to "ruin his 'reputation,' 'future' and 'career'" if he continued to raise his concerns about TPG's potential violation of securities laws and misrepresentations to investors that led to "TPG's investors being defrauded of millions of dollars in fees and expenses." He claims the firm fired him after he "felt he had no choice" and reported apparent violations to the SEC.

TPG in January sued Levine, former global head of public affairs at TPG and a Bush White House spokesman, in federal court in Texas for allegedly taking confidential documents and threatening to go to the press to hurt the firm.

Reuters said Levin's whistleblower is suit is "almost without precedent in the tight-knit world of private equity."

Levine, who claims the firm owes him more than $738K in non-cash compensation, has called TPG's suit against him a "baseless and retaliatory" measure. He has sued the firm in federal court in California.

In the suit, Levine outlines his internal struggle to build up the firm's PR operation ahead of an initial public offering, alleging that top executives promised a partnership in the PE firm if he staffed the PR unit with contractors and billed it out to portfolio companies and LPs, rather than the main TPG firm. Levine claims he repeatedly expressed reservations about such a move's compliance with SEC regulations.

TPG fired Levine at the end of 2014.