KPMG is facing a three-month freeze on new federal government contracts amid a worsening scandal over the treatment of a whistleblower, with the Greens now referring the beleaguered company to the national anti-corruption watchdog.

Accounting firm KPMG is engulfed in a scandal that has seen several senior leaders quit and ASIC launch an investigation into the firm's business dealings.

The firm has agreed to stop bidding for Commonwealth work while the Finance Department investigates its handling of a whistleblower complaint.