Thailand's ministry of digital economy and society will file a criminal complaint of defaming the country's monarchy against banned opposition politician Thanathorn Juangroongruangkit, the ministry said on Wednesday.
The digital ministry did not specify what actions the lese majeste complaint would cite, but two ministry officials told Reuters they were related to comments Thanathorn had made about the government's vaccine strategy.
The move could mark the highest-profile lese majeste case since a wave of anti-government protests emerged last year and extended to criticism of King Maha Vajiralongkorn over allegations of meddling in politics and taking too much power.
Thailand's royal defamation law, known as lese majeste, punishes defaming or insulting the Thai king by up to 15 years in prison.
The complaint against Thanathorn under Article 112 of the Thai criminal code will be filed on Wednesday afternoon, according to an official ministry memo sent to reporters.
It comes two days after Thanathorn, who a court last year banned from politics for 10 years, criticised Thailand's Covid-19 vaccine strategy for being too reliant on a company owned by the Crown Property Bureau, which is under the king's personal control.
Prime Minister Prayuth Chan-ocha, who first took power in a 2014 military coup, on Tuesday vowed to prosecute "distorted" information about the vaccine strategy.
Thanathorn could not immediately be reached for comment, but the Progressive Movement he heads said there was no insult in his comments at the group's event titled "Royal Vaccine: Who Benefits and Who Doesn't?" that was broadcast on Facebook Live.
"It's obvious that 112 is being used again as a political tool," Pannika Wanich, Thanathorn's colleague and one of the group's leaders, told Reuters.
The Progressive Movement was formed after a court last year ruled to dissolve Thanathorn's Future Forward Party, which came in third in 2019 elections held five years after Prayuth's coup.
Opposition parties accused Prayuth's junta of designing the elections to ensure he remained in power. Prayuth's pro-military party has said the elections were free and fair.