Prosecutors will decide on Nov 4 whether to indict Progressive Movement founder Thanathorn Juangroongruangkit over his criticism of the government's Covid-19 vaccination programme as well as his alleged violation of the lese majeste law.
Mr Thanathorn's lawyer Krissadang Nutjaras disclosed the date on Tuesday after learning of it at the Office of the Attorney-General, he said.
The date was set after Mr Thanathorn appealed for justice and requested the prosecutors clarify several matters with a direct bearing on the case.
Mr Thanathorn faces three charges pertaining to the violations of Section 112 of the Criminal Code, or the lese majeste law, the Computer Crime Act and the defamation law.
The charges were filed with the police against the movement's leader by Apiwat Khanthong, chairman of the government-appointed committee investigating the spread of disinformation about the execution of the prime minister's and cabinet ministers' duties.
The charges came after Mr Thanathorn was held to account over the release of a video recording of a Facebook Live session on Jan 18 in which he criticised the government for being too reliant on Siam Bioscience to meet its vaccination needs.
Siam Bioscience, a pharmaceutical firm founded by King Rama IX some 12 years ago, received the right to produce AstraZeneca's Covid-19 vaccine in Thailand, under a technology-transfer agreement.
The session, titled "Royal Vaccine: Who Benefits and Who Doesn't?" urged the government and the firm to publicly reveal the vaccine-production agreement to prove the procurement was being done in a transparent manner.
Following Mr Thanathorn's comments, the firm insisted it was selected because it met AstraZeneca's stringent production criteria.
On Tuesday, Mr Krissadang said the prosecutors have been asked to clarify whether Mr Apiwat had the authority or was qualified to seek Mr Thanathorn's prosecution.
The lawyer added the case may also duplicate one filed by a ministry on a similar charge against Mr Thanathorn.
He was understood to be referring to the petition filed by the Ministry of Digital Economy and Society after Mr Thanathorn's recorded session was released, asking the Criminal Court to order the removal of the video.
The court ruled against the petition, finding the video's content was not in violation of Section 112 of the Criminal Code.