Many pro-democracy protesters have covered their faces to hide their identities and protect themselves from tear gas. The ruling comes at a time when it is compulsory to wear masks in the city due to the coronavirus.
Hong Kong's top court has ruled that the city government's decision to invoke a colonial-era law to ban face masks at demonstrations and public meetings during the height of the 2019 pro-democracy protests was legal.
"The ambit of the power to make subsidiary legislation under the ERO in a situation of emergency or in circumstances of public danger, although wide and flexible, was not unconstitutional," the judges ruled on Monday.
They added that banning face masks at both permitted and illegal rallies was proportionate since it was aimed at "the prevention and deterrence of violence before a peaceful public gathering had deteriorated into violence."
Many anti-government protesters wore face masks last year to reduce the risk of being identified and prosecuted by authorities for taking part in peaceful marches or violent clashes with the police. The masks also protected them from tear gas used by police to disperse the massive crowds.
In October last year, Hong Kong's pro-Beijing Chief Executive Carrie Lam banned anyone from covering their face at public rallies using the Emergency Regulation Ordinance, a colonial-era law, for the first time in 50 years.
Opposition lawmakers and activists opposed the anti-mask law as well as the use of the emergency law. They lodged a judicial review last year, arguing the government's move was in breach of Hong Kong's Basic Law — the city's mini-constitution.