The libel suit would not be settled out of court and the AEC would lodge a complaint with police soon against Chaturon for his remark, he said.

"This is not a threat against those who want to criticise our work. People can criticise - but not slander us,'' he said.

AEC secretary Kaewsan Atibodhi, meanwhile, defended the agency. He said it had not repeatedly taxed the Shinawatra family in regard to Ample Rich's stake in Shin Corp.

Kaewsan was responding to a lawyer for deposed prime minister Thaksin Shinawatra, Noppadol Pattama, who threatened to sue the AEC for "repeatedly taxing" Panthongtae and Pinthongta Shinawatra, Thaksin's children.

Kaewsan said: "They can take us to court, but we believe we did the right thing. And we have no intent to cause them any damage. We are just protecting the country's interest."

He said Ample Rich had to pay the full 30 per cent income tax because it conducted business in Thailand. Ample Rich had already paid 10 per cent but it had to pay 20 per cent more - including 7 per cent of profits from overseas.

"This is not to tax repeatedly, but to punish Ample Rich for not paying tax. If you are trying to walk around the bush, you have to be punished," he said.

In another AEC case, former agriculture minister Sora-at Klinpratoom testified  over the Central Lab case. He denied being involved in the project, saying he had left his post before it materialised.