Rong Chhun, the leader of the Cambodian Confederation of Unions, was arrested in July after accusing the government of "irregularities" over the demarcation of the eastern border with Vietnam. He said the newly agreed borderline encroaches on some locals' farmland.
Opposition politicians have long accused strongman premier Hun Sen of ceding territory to Vietnam, harnessing the long-running unresolved border issues between the two countries to whip up nationalist sentiment against his administration.
Rong Chhun, who has been in pre-trial detention since his arrest, faces up to two years in prison if found guilty of incitement to commit a felony or cause social unrest.
He appeared at the Phnom Penh municipal court alongside two other people, who were arrested during protests demanding his release and face the same charges, defence lawyer Sam Sokong told AFP.
Rong Chhun was questioned about his border comments and shown a video clip of him meeting with Cambodian people at the border, he said.
"Rong Chhun told the court that it is his right to express opinions about social issues," Sam Sokong said, adding that the court then adjourned the hearing to February 3.
"Rong Chhun denied the charges. He told the court that it is not a crime, it is just an expression of his opinion."
Since the election in July 2018, when Hun Sen's party won every parliamentary seat in a vote without a credible opposition, the Cambodian authorities have stepped up arrests of former opposition party members, human rights defenders and dissenting voices.
The same court is also trying around 150 opposition figures and activists on treason and incitement charges that rights groups slammed as a politically motivated sham.
While many opposition politicians have fled Cambodia fearing arrest, the country's main opposition leader Kem Sokha is facing a separate treason trial, which has been indefinitely delayed since March last year.
Hun Sen is one of the world's longest-serving leaders, maintaining a 36-year grip on power with methods that critics say include jailing political opponents and activists. - AFP
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