Mr Ruangkrai said that the Democrat Party had posted eight articles on its website asking eligible voters not to vote for the Pheu Thai Party between Dec 26 and Jan 20.
Two of the articles involved Democrat leader Abhisit Vejjajiva and six involved party spokesman Chavanond Intarakomalyasut, he said.
He said a post on Jan 17 accused Pheu Thai of buying votes while another on Jan 20 accused Pheu Thai politicians of corruption and said the Feb 2 election was intended to whitewash caretaker Prime Minister Yingluck Shinawatra.
Mr Ruangkrai argued that the Democrat executive committee was probably involved in the posts since they appeared shortly after the part's general assembly at the end of last year.
This could violate of the Political Party Act and election law, he said.