Opposition leader Chonlanan Srikaew said on Monday that the legalisation of cannabis violates Section 92 of the organic law on political parties and had been designed to win votes.
"The party will file a petition with the Election Commission," he said.
He added that the opposition parties are studying the petition details closely and expect to have clarity by November 1.
Chonlanan said the opposition is against the legalisation of cannabis because it is having an adverse impact on society.
Removing cannabis and hemp from the category 5 narcotics list was one of the policies put forward by Bhumjaithai as it was campaigning for votes in 2019.
Public Health Minister Anutin Charnvirakul, who is also Bhumjaithai leader, issued a ministerial edict declaring cannabis and hemp legal on June 9 this year, which allowed the public to grow the plants commercially.
Chonlanan said the opposition parties will also ask the Administrative Court to overturn the edict, as it leads to the misconception that cannabis is safe to use and has medical benefits.