Hong Kong police on Sunday detained 47 pro-democracy activists on charges of conspiracy to commit subversion under the city’s national security law, in the largest mass charge against the semi-autonomous Chinese territory’s opposition camp since the law came into effect last June.

The former lawmakers and democracy advocates had been previously arrested in a sweeping police operation in January but were released. They have been detained again and will appear in court on Monday, police said in a statement.

They allegedly violated the national security law that was imposed by Beijing for participating in unofficial election primaries for Hong Kong’s legislature last year.

The defendants include 39 men and eight women aged between 23 and 64, police said.

The move is part of a continuing crackdown on the city’s democracy movement, with a string of arrests and prosecutions of Hong Kong’s democracy proponents — including outspoken activists Joshua Wong and Jimmy Lai — following months of anti-government protests in 2019.

The pro-democracy camp had held the primaries to determine the best candidates to field to win a majority in the legislature and had plans to vote down major bills that would eventually force Hong Kong leader Carrie Lam to resign.

In January, 55 activists and former lawmakers were arrested for their roles in the primaries.

Authorities said that the activists’ participation was part of a plan to paralyze the city’s legislature and subvert state power.

The legislative election that would have followed the unofficial primaries was postponed by a year by Lam, who cited public health risks during the coronavirus pandemic. Mass resignations and disqualifications of pro-democracy lawmakers have left the legislature largely a pro-Beijing body.

Among those arrested on Sunday was former lawmaker Eddie Chu. A post on his official Twitter account confirmed that he was being charged for conspiracy to commit subversion and that he was denied bail.

“Thank you to the people of Hong Kong for giving me the opportunity to contribute to society in the past 15 years,” Chu said in a post on his Facebook page.

Another candidate in the primaries, Winnie Yu, was also charged and will appear in court on Monday, according to a post on her official Facebook page.

American lawyer John Clancey, a member of the now-defunct political rights group “Power for Democracy” who was arrested in January for his involvement in the primary, was not among those detained on Sunday.

“I will give full support to those who have been charged and will be facing trial, because from my perspective, they have done nothing wrong,” Clancey told reporters.

The security law criminalizes acts of subversion, secession, terrorism and collusion with foreign powers to intervene in Hong Kong’s affairs. Serious offenders could face a maximum punishment of life imprisonment. Nearly 100 people have been arrested since the law was implemented.