A Hong Kong court on Monday sentenced pro-democracy media tycoon Jimmy Lai to 20 years in prison in one of the highest-profile cases brought under China’s national security law, which critics say has effectively silenced opposition in the city.

Three government-appointed judges convicted Lai, 78, of conspiring with others to collude with foreign forces to endanger national security, as well as conspiring to publish seditious material. He was found guilty in December.

The court spared Lai the maximum sentence of life imprisonment, but given his age, the prison term could see him remain behind bars for the rest of his life.

Lai, the founder of the now-defunct Apple Daily newspaper, has been one of Beijing’s most outspoken critics and a prominent supporter of Hong Kong’s pro-democracy movement.