Thepthai Senpong, the personal spokesman of Prime Minister Abhisit Vejjajiva, got a parcel full of excrement Monday morning.
Party officials did not screen the parcel but they passed it on to Thepthai at 10 am.
When the parcel was opened, it was found to contain a letter and a plastic bag.
Thepthai opened the letter to read immediate and it was too late for him to stop his aides from opening the bag.
The party was filled with bad smell once the bag was opened and the hands were of the aides were soiled.
The smell caused a commotion among reporters and party officials nearby.
The letter was said: "I send this letter to praise you that you have been acting like a dog loyal to your boss. I heard someone has already sent you a muzzle. I think the muzzle is too inconvenient for you so I am sending a little excrement for you to eat as a dog always likes to eat excrement."
The letter carries the sender address as "the Association of Upper Northeastern People in Udon Thani's Khumpawapi" district.
It was signed as "Kan Muangkum".
Thepthai said "The package tainted my men's hands, and there was the smell. But I don't feel bad. This is a way for people to express opinions."
He said he will keep the letter to hold an exhibition of what he has received from his political opponents.