A Hong Kong court sentenced activist Edward Leung to six years in prison Monday for his part in a violent nightlong clash with police over illegal street food hawkers two years ago. Leung, 27, was among a generation of young political activists who emerged after 2014’s failed nonviolent protests over Beijing’s decision to restrict elections. His sentence shows the hard line authorities are taking toward those advocating for more open politics in the former British colony.

The South China Morning Post reported that Lo Kin-man, charged alongside Leung, was sentenced to seven years on a conviction for rioting, while a third man, Wong Ka-kui, 27, was given a sentence of 3 years. The Feb. 8-9, 2016, outbreak of violence in the city’s working-class Mong Kok district was the most serious opposition to local authorities in decades.

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Leung has been an advocate of independence for Hong Kong, which became part of China in 1997 after more than a century of British rule. China guaranteed a 50-year transition period under which Hong Kong would retain considerable autonomy and keep the rule of law and its own legal and financial system. However, the ruling Communist Party has made it clear those liberties are limited by its bottom line on sovereignty over the territory.

Chinese President Xi Jinping warned in a speech last year that any activities in Hong Kong seen as threatening China’s sovereignty and stability would be “absolutely impermissible.