A San Francisco accounting firm is facing a $5 million lawsuit filed by a whistleblower, who alleges the firm engaged in “intentional tax fraud” for one corporate client and “substantially” understated tax liability for a second client.

Tax accountant Gary Winston said he was fired for making the problems known to the principals of the firm, Shea Labagh Dobberstein, which has offices in San Francisco and San Mateo, CA. The principals signed off on the tax returns despite the information, the suit says.

The clients were not named in court papers, and Winston's attorney would not comment on the case regarding the size of the alleged tax fraud or evasion, the San Francisco Chronicle reported.

The firm filed a motion to dismiss the case on the basis that it was inappropriate for the whistleblower protection law, but the contention was dismissed by Superior Court last month. A trial date is pending, the Chronicle reported.