Jimmy Lai, the founder of Hong Kong’s pro-democracy newspaper Apple Daily, was on Monday arrested after scores of police raided the paper’s headquarters in the highest-profile case yet under Hong Kong’s new national security law.

Lai, 71, was arrested along with his sons and four other executives of the company.

The police said the arrests were for offenses that included collusion with a foreign country to endanger national security and fraud.

The media mogul has been a longtime supporter of the campaign for democracy in the Chinese-ruled city and oftentimes a vocal critic of Beijing.

The national security law came into effect June 30 and is widely seen as a means to stifle dissent under its sweeping powers to enforce crimes of secession, subversion, terrorism and collusion with a foreign country.

Apple Daily’s reporters shared a livestream on social media showing around 200 police officers entering their offices, some of whom were seen rifling through reporters’ desks and then carting off stacks of boxes of evidence.