Rubber growers from the South plan to gather in the capital to pressure the military regime into propping up falling prices in all central rubber markets in the South, according to an informed source.
They are mulling a protest at the Agriculture Ministry, the source added.
At a recent meeting, rubber growers agreed the rubber price problem had reached a point where they have to do something.
Prime Minister Prayut Chan-o-cha offered no relief, but said the government remains concerned about the agricultural sector as some crops, particularly rubber, still have falling prices.
"Dropping rubber prices are primarily because of market fundamentals," he said. "Many buying countries have reduced their purchases of natural rubber while global oil prices are still as low as US$50 per barrel".
He said the government has been trying to increase domestic consumption for rubber, especially through campaigns calling for private tyre companies to raise their production.
Jatuporn Terachusong, president of the Yungthong rubber plantation fund cooperatives in Lan Saka district of Nakhon Si Thammarat, said rubber growers' incomes have slumped by more than half while the cost of living continues to rise.
The bidding prices for rubber in the South's three major central rubber markets continued to drop Tuesday, said another source.
The price of unsmoked rubber sheets offered by the winning bidder at the central rubber market in Hat Yai district of Songkhla dropped by 52 satang to 44.38 baht per kilogramme Tuesday.
A similar price for unsmoked rubber sheets was offered by the bid winner at Surat Thani central rubber market, down 63 satang to 44.58 baht per kg.
The price offered by the winning bidder at the Nakhon Si Thammart central rubber market was 63 satang per kg lower.
Wuth Rakthong, a representative of Phuang Phromkhon cooperatives in Surat Thani's Khian Sa district, said all rubber growers' cooperatives in the province have decided to boycott a workshop scheduled to be held today in Krabi, which is expected to be attended by leaders of about 40 agricultural institutions nationwide.
Mr Wuth criticised the establishment of a fund by five giant companies to purchase rubber at the southern central rubber markets, saying the fund, which is aimed at helping improve rubber prices, is instead causing volatility in its prices.
He also lashed out at the Rubber Authority of Thailand (RAT) and the government, saying the RAT never paid sufficient attention to ensuring price stability for rubber, while the government's move to spend more than 2 billion baht to support cooperatives to build rubber processing houses has proved to be a waste of taxpayers' money.
In Nakhon Si Thammarat, Nantachat Chaihao, president of a network of rubber growers in Tha Sala district, said while the average cost of growing and producing rubber stands at 62 baht per kg, it now sells for only 45 baht to 46 baht per kg.
On Monday, Sunthon Rakrong, president of an association of rubber growers in the 16 southern provinces and secretary-general of the network of rubber growers of Thailand, posted on his Facebook harsh criticism of the five experts who represent rubber growers nationwide on the RAT's board.
Although they occupy one-third of the seats on the RAT's board, they have done nothing to help rubber growers especially at a time when prices are falling, Mr Sunthon said.
He said the performance of the five board members over the past two years has dismayed rubber growers across the country.