Hong Kong’s embattled leader invoked emergency powers to ban face masks at the city’s pro-democracy protests, threatening offenders with a year in jail if they prevent themselves from being identified by police. Chief Executive Carrie Lam announced the move Friday morning following widespread violence this week marking the 70th anniversary of Communist rule in China. Lam said violence was “destroying the city” and authorities could not “just leave the situation to get worse and worse,” the BBC reports. The mask ban will come into effect midnight Friday. However, it is likely to be difficult to enforce—mask-wearing activists marched Friday afternoon as the ban was being announced and urged others to defy the government. The emergency law invoked by Lam hasn’t been used in more than 50 years.