Holding posters seeking for justice and for unpaid rice, they called on provincial authorities for prompt action to remedy their troubles.
Their leader Pinit Chairat said farmers sold their rice to Nitipol Sahakarn Kaset under the 2013 rice pledging scheme at the total sum of 9.5 million baht.
But the firm did not issue documents to show they have pledged the rice with it.
He said farmers had been paid 4.2 million while the remaining 5.3 left unpaid.
They wanted their money back immediately, he said.
The assistant governor later came out to receive their complaint and promised to escalate the fraud case against the firm.
They said so far three people have been charged with fraud and two mills which bought rice from farmers also are facing investigation.
Meanwhile, Prime Minister Gen Prayut Chan-ocha announced payment of the rice farming subsidy of 40 billion baht will begin October 20, and cautioned landlords against exploitation of the scheme, farmers said the legal action threat could not work as they still have to rent land to farm.
Gen Prayut described his 1,000 baht per rai per household a non populist policy, and vowed to tackle landlords drastically if they forced farmers for share of the subsidy.
He said the subsidy was not much and even meant nothing for the rich, but this small amount of money meant so much for farmers.
He cautioned against mishandling of the scheme and the exploitation of the scheme by landlords.
Under the short-term remedy scheme, a household of farmers owning not more than 15 rai of farmland will receive 1,000 baht as subsidy from the government as farming cost. For those who have over 15 rai, the maximum payment is capped at 15,000 baht subsidy.