A Taiwanese court has sentenced four former staffers of the ruling Democratic Progressive Party (DPP) to prison for spying for China, in one of the island’s highest-profile espionage cases.

Among them was Huang Chu-jung, a former aide to President Lai Ching-te during his vice-presidency, who received the heaviest sentence of 10 years plus a fine for espionage and money laundering.

Huang was accused of relaying sensitive information to Chinese intelligence via encrypted apps and directing others to gather intelligence from senior officials, including former foreign minister Joseph Wu.

Chiu Shih-yuan, ex-deputy head of the DPP’s Taiwan Institute of Democracy, was sentenced to six years and two months after pleading guilty.

Two other aides received shorter terms, while prosecutors may appeal for tougher sentences.

President Lai has tightened security measures against suspected pro-China infiltration, labeling Beijing a “foreign hostile force” earlier this year, The Guardian has reported.

Taiwan, which Beijing claims as its territory, has faced growing espionage, disinformation, and “cognitive warfare” campaigns as China seeks to weaken resistance to unification.