In legal papers filed Friday, lawyers argue that Puea Thai's campaign involved former Prime Minister Thaksin Shinawatra and other people who have been banned from politics, the Bangkok Post reported. Thaksin, who has been living in exile since he was ousted by a 2006 military coup, is the brother of Pheu Thai leader Yingluck Shinawatra, who is about to become prime minister.
A spokesman for the Democrat Party said it is not involved in the legal challenge, The Wall Street Journal reported.
Prompong Noparrit, a spokesman for Puea Thai, said Thaksin sometimes discusses politics with his sister and other party leaders. But he said Thaksin is in no way a leader of the party.
Puea Thai won an outright majority of 265 seats in the 500-member Parliament. Some smaller parties have joined its coalition, bringing its majority to more than 300.