Jailed former opposition leader Kem Sokha will be brought to the Appeal Court on Tuesday to challenge a decision made in early March to extend his pre-trial detention by six months.

Sokha, the former president of the Cambodia National Rescue Party, has languished in a Tbong Khmum prison since his midnight arrest on September 3 for alleged “treason.” The arrest followed the release of a 2013 video in which Sokha talks with supporters abroad about having received foreign assistance to plan his political career.

Appeal Court spokesman Touch Tharith confirmed that Sokha would be present at court on Tuesday.

“The Appeal Court has already sent the summons, according to the procedure, to his lawyers and to him [Sokha] to come to join the hearing,” he said.

Sokha has left prison only once since his arrest, for a bail hearing at the Appeal Court in February. His party was dissolved in November following a complaint from the Ministry of Interior, with 118 party officials, including Sokha, banned from the political arena for five years.