A court in Cambodia sentenced activist Pen Mom on Thursday to five years in prison for a plot to overthrow Prime Minister Hun Sen’s government. A total of 17 activists that oppose the government have been jailed since late July.

The court found Pen Mom guilty of conspiring with Sam Rainsy, an opposition party founder, to overthrow the government. Pen Mom was a former official in the Cambodia National Rescue Party (CNRP), a disbanded party that merged with the Sam Rainsy Party and the Human Rights Party.

Hun Sen has ruled Cambodia since 1985 and is one of the world’s longest-serving prime ministers. Sen is part of the Cambodian People’s Party (CPP). After the CNRP began to gain momentum and won more seats in the National Assembly, members of CNRP began to get arrested. CNRP supporters accuse Hun Sen and his party of tampering with past election results. The Supreme Court ultimately disbanded the CNRP before the 2018 national election.

Pen Mom’s arrest follows a series of arrests of activists, including prominent union leader, Rong Chhun. Authorities arrested Chhun on July 31 because he was advocating for land rights for Cambodians living near the border of Vietnam. Authorities additionally arrested youth and environmental advocates in August for attempting to peacefully protest Chhun’s arrest.