The decision is a setback for the victims and rights advocates who had high hopes for a favorable resolution to the case.
The hearing was held behind closed doors with only Kem Sokha’s legal team allowed to attend.
A government spokesman said offenders could also receive a fine of more than $15,000.
Kem Sokha, who has diabetes and high blood pressure, has been in prison since early September.
Hun Sen said Cambodia needed the Chinese workers referred to by Min due to a lack of “human resources”.
Foreign nationals from Britain, Canada, the Netherlands, Norway and New Zealand arrested during raid at pool party near ancient Angkor Wat temple.
Arrest of 68-year-old James Ricketson on espionage-related charges coincides with crackdown on dissent by autocratic Prime Minister Hun Sen.
Sean Pengse frequently criticized Cambodia's policy on border demarcation with Vietnam, saying the government did not comply with the Paris Peace Agreement
The Cambodian Labor Confederation (CLC) is led by Ath Thorn, one of Cambodia’s most prominent unionists.
Interior Minister Sar Kheng comments came after the country’s top military police official labeled the CNRM a terrorist group.
The case against Laysreng was filed in October by Ky Tech, a lawyer for Hun Sen who was recently appointed to the CPP’s Central Committee.
In total, 342 additional members were added to the Central Committee, according to a resolution published by the CPP.