The 29-year-old Wong, one of the most famous faces in Hong Kong's effectively crushed democracy movement, is already serving a prison sentence of almost five years for subversive activities and was due to be released next year.
He is now accused of having urged foreign countries, individuals or institutions to "impose sanctions or blockades" against Hong Kong and China in 2020.
Human rights organizations believe the new charges, which could lead to Wong being sentenced to life in prison, are aimed at keeping him behind bars for as long as possible.
