Bhumjaithai leader Anutin Charnvirakul said he had spoken to Prime Minister Srettha Thavisin about the party's concerns over the Ministry of Public Health's plan to re-list cannabis as a narcotic.
Mr Anutin said he had told Mr Srettha the proposal lacks proof to justify the re-criminalisation of the plant.
He urged the prime minister to carry out more studies before relisting cannabis as a narcotic.
Mr Anutin said he was puzzled by the government's U-turn on the issue, noting the committee which is pushing for cannabis to be relisted as a narcotic is made up of the same people who wanted cannabis to be decriminalised two years ago.
He called on the committee members to explain to the Public Health Ministry why cannabis needs to be taken off the narcotics list.
The Bhumjaithai leader claimed Mr Srettha said he was open to further discussions on the matter and listening to Bhumjaithai's concerns about the cannabis relisting proposal.
