The policy guarantees Thai rice farmers a much higher price than on the global market, but critics say it is too expensive and vulnerable to corruption.
The commission has already charged one minister, and is investigating others.
The news comes as Ms Yingluck already faces intense pressure to resign.
Anti-government protesters have been marching through the capital, saying they will shut it down until their demands are met.
They accuse her government of being under the control of her brother, ousted former leader Thaksin Shinawatra.
They say they want an unelected "People's Council" instead, to reform the electoral system.