The order was signed by Wattanasak Sur-iam, the department director-general, and sent to the president of the palm oil extraction association on Wednesday.
In the letter, Wattanasak said that officials from his department had visited a province, which is a large producer of oil palm fruit, and held a meeting with representatives of oil palm farmers, intermediary palm buyers, and oil palm extraction plants on Tuesday.
The order did not reveal the name of the province.
Wattanasak said the meeting resolved to require middle-man buyers to buy the fruit from farmers at a minimum of 4.50 baht per kg.
If the fruit is of premium quality, the buying price must be raised accordingly, the order stated.
The order stated that anyone found to be buying the fruit at below the set price, would face a maximum jail term of seven years, or a maximum fine of 150,000 baht, or both.
The order also required operators of the extraction plants to report their operations to the department on a daily basis. The figures should state the amount of palm fruit purchases, the purchase rate and the quantity of extracted oil.