(Bloomberg) -- Hong Kong police charged 47 opposition activists with violating the city’s national security law, taking formal action against them less than a week before China’s highest-profile annual political meeting.

Of the 55 opposition figures initially arrested in January, 47 were charged with conspiracy to commit subversion on Sunday. They had previously been facing allegations of subversion. It is the largest mass charge under the new law since it went into effect last year.

The activists will be detained overnight and will have to appear in court Monday, the police said in a statement. Some had been asked to report to the police’s national security branch on Sunday, more than a month earlier than scheduled.

The former lawmakers and activists were arrested in January on suspicion of subversion for their roles in helping organize a democratic primary contest over the summer that drew more than 600,000 voters.

Police allege the primary, as well as plans to use a provision in the city’s mini-constitution to vote down the budget and force the Hong Kong chief executive’s resignation, were part of an illegal attempt to paralyze the city’s government. The election was eventually postponed by a full year, with the government citing the coronavirus.

Beijing is tightening control over the Asian financial center after a historic wave of democracy protests gripped Hong Kong for months in 2019. The national security law carries sentences as long as life in prison depending on the severity of the offense.

While almost 100 people have been arrested under the new law, prosecutors had previously only brought charges against 10 of them. The most prominent is media mogul Jimmy Lai, who has been denied bail and is awaiting trial on charges that he colluded with foreign powers to impose sanctions or engage in hostile activities against Hong Kong or China.

China’s annual parliamentary pageant -- the National People’s Congress -- opens Friday in Beijing. Reforms to Hong Kong’s electoral system that would give Beijing more control could come at this year’s event, according to Hong Kong leader Carrie Lam.

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