The rally has been called after government failed to meet the demands of farmers who have been protesting for more than a week.
The government has offered to raise the raw sheet rubber price to 80 baht per kilogramme and subsidise rubber cultivation at 1,260 baht per rai up to a maximum of 10 rai per farmer.
The southern protesters are demanding a guaranteed 120 baht a kilogramme for smoked rubber sheet and at least seven baht for palm oil.
The rubber price currently stands at 60 baht per kg, while the palm oil price is around two baht.
The standoff between farmers and the authorities intensified after a shooting at the site of protests in Cha-uat district, which killed Sirichai Boonnuwong, a guard, and seriously wounded Sithisak Jai-ngam, a protester on Sunday.
The Tuesday rallies are to take place at the Co-op in Surat Thani's Phunphin district, Ban Toon in Cha-uat district of Nakhon Si Thammarat and three provincial halls in Chumphon, Krabi and Trang. There may also be a rally of rubber growers from Rayong, police spokesman Piya Uthayo said on Monday.
There were no reports of protests being planned in Ranong, Phangnga or Phuket in the South or in any other regions.
The police spokesman warned protesting farmers not to blockade roads or the railway, which would paralyse transportation in the southern region. Police will try control the protests peacefully, he added.
Pol Maj Gen Piya cited police intelligence as indicating that some protest leaders in the South were linked to the People's Democratic Force to Overthrow Thaksinism, set up to oust the current government and oppose former prime minister Thaksin Shinawatra.
But Praphan Chumuang, a protest leader, dismissed the claim, saying that the rally was not politically motivated and had no backing from political parties or groups.
"It is about the issue of our living conditions. The government dislikes the opposition but that is not the farmers' business," he said. "We only need a better answer from the government on how to help rubber and oil palm farmers. They should come down to talk to us."
Farmers in the south have been staging protests since Aug 23 and planned to step up the rally to put more pressure on the government.
Representatives of rubber planters of 17 northern provinces on Monday reaffirmed they will definitely not set up a road blockade in Pichai district of Uttaradit as earlier planned - at least, not yet.
Pongnimit Kaewdaeng, chairman of a network of rubber planters of Uttaradit, made the announcement after a meeting of about 20 leading rubber farmers of 17 northern provinces in Thong Saen Khan district on Monday morning.
The farmers agreed to give the government until Sept 13 to deal with the issues facing farmers, he said.
Mr Pongnimit said that if by Sept 13 the government had done nothing the rubber farmers would take action. He did not elaborate on what that would entail.
He said the northern rubber growers were not sure if the government was sincere about solving their problems stemming from low prices for their products. If it was, the protest in Nakhon Si Thammarat in the South would not have escalated to a point where one protester had been killed and another wounded, he said.
On the shooting in Cha-uat district which killed Sirichai Boonnuwong, a guard, and seriously wounded Sithisak Jai-ngam, a protester, Pol Maj Gen Piya said police had interviewed four witnesses, including a doctor, and would question six others, most of them security guards.
He said Pol Gen Pansiri Prapawat, a deputy police chief, had been assigned to go to Nakhon Si Thammarat to conduct an in-depth investigation.
Police are to apply to the court for an arrest warrant for the main suspect in the shooting of the two rubber protesters, Thai Rath online reported.
Rachot Yensuang, in charge of the investigation into the incident, was speaking after visiting Mr Sithisak at an intensive care unit of Maharaj Nakhon Si Thammarat Hospital, the report said.
He said a picture of the suspect was shown to Mr Sithisak, who confirmed the man in the picture was the person who shot him and killed Sirichai Boonnuwong.
Pol Gen Rachot identified the man in the picture as Kiatisak Kaewprom, saying that he had fled the district.
He said a quarrel during a drinking session near the Ban Toon railway crossing led to the shooting.
Police were still looking for Mr Kiatisak, he added.