Democrat chief adviser Chuan Leekpai has rejected the invitation by Chartthaipattana chief adviser Banharn Silpa-archa to join the political reform assembly initiated by Prime Minister Yingluck Shinawatra.
Mr Banharn and other leading members of Chartthaipattana called on Mr Chuan at the Democrat Party headquarters on Thursday.
Mr Banharn is inviting leading figures experienced in political and other affairs to join the assembly.
After a meeting last more than two hours, Mr Banharn refused to reply to reporters' questions, saying only that Mr Chuan had the same attitude as Democrat Party leader Abhisit Vejjajiva.
Mr Abhisit earlier turned down the invitation when approached by Mr Banharn.
Mr Banharn said, however, that Mr Chuan had given him a lot of useful information and asked him to adhere to the principle of good governance.
Mr Chuan said afterwards that he had turned down Mr Banharn's invitation and explained to the Chartthaipattana chief adviser why the country is in its present state.
He said the Democrat Party was not the cause of the country's problems.
The government had failed to eliminate the conditions - including corruption, interference in the work of independent agencies, and acts of lese majeste - which were cited by the military as the reason for the Sept 19, 2006 coup, Mr Chuan said.
Mr Chuan said he explained to Mr Banharn that the problems with rubber farmers in the South derived from the fact the government discriminated against them.
He accused the government of wrongfully holding to the belief that politicians in the region were behind the rubber farmers' protest.
The Democrat Party had never approved of the farmers acting in a wrongful manner, including the blockade of the rail track, Mr Chuan said.