Sontirat Sontijirawong, the commerce minister who chairs the commission, said it had decided to send a letter to the operators, ordering them to abide by the law and stop their misbehaviour.
The Trade Competition Commission found some operators, which gather agricultural products or purchase fruit, still unfairly fix or maintain prices since the new trade competition bill has taken effect.
If the operators disagree with the order, they can appeal and file a case against the commission's order to the administrative court within 60 days after receiving the order.
If operators continue, they could be fined up to Bt6 million or a daily fine of Bt300,000.
Sontirat said that the Ministry of Commerce would also send letters to other operators telling them to abide by the new bill.