
"Suthep's refusal to step down reflects his poor ethical standards, worst than rotten canned fish," Pheu Thai spokesman Prompong Nopparit said.
Last week the Election Commission disqualified Suthep's younger brother Thani for violating election rules while campaigning for the presidency of the Surat Thani Provincial Administration Organisation.
The EC also requested police to look into Suthep's role when Thani gave handouts to his constituents two years ago. It was suspected that Suthep was present.
Suthep said he would not engage in a war of words with the main opposition party.
"Please wait for a few more days. Facts will come out to let everyone understand the true situation," he said in reference to his legal wrangling.
He said he was prepared to defend his name in court and would not comment on the case at this stage.
Suthep had hosted a luncheon for 15 ranking Democrats.
He said he wanted to exchange views on the government's progress in achieving its goals.
"This is just a good day to have lunch together since we have not had a chance for the past five months working in the government," he said.
Seen at the gathering were Deputy Prime Minister Korbsak Sabhavasu, Culture Minister Teera Slukpetch and Deputy Commerce Minister Alongkorn Ponlaboot, who have come under attack for their job performance.