China insisted Tuesday it held the sole authority to rule on constitutional matters in Hong Kong, as it condemned a decision by the city’s high court to overturn a ban on face masks worn by pro-democracy protesters.

The statement could further fan the flames in Hong Kong after months of violent protests over concerns that Beijing is chipping away at the autonomy of the financial hub.

The ban on face coverings came into force in October, when the city’s unelected pro-Beijing leader invoked colonial-era emergency powers legislation for the first time in more than 50 years.

The move was seen as a watershed legal moment for the city since its 1997 return by Britain to China — but has been largely symbolic.

The city’s high court ruled on Monday that the government ban on face masks was unconstitutional as it unduly infringed on Hongkongers fundamental freedoms. But Beijing said the judicial branch of the special administrative region had overreached.

Zang Tiewei, spokesman of the legislative affairs commission of the National People’s Congress standing committee said only the NPC had the right to rule on whether a law is in accordance with the Basic Law — the city’s mini-constitution.

“No other institution has the right to make judgements or decisions,” Zang said, according to a state media report posted on the NPC’s website.

Zang said the ruling had “severely weakened the governance” of Hong Kong Chief Executive Carrie Lam and the city government.

In fact, Zang’s assertion would appear itself to contradict Article 85 of the Basic Law, which states: “The courts of the Hong Kong Special Administrative Region shall exercise judicial power independently, free from any interference.”

It would also appear to contravene the Sino-British Joint Declaration, the agreement under which Hong Kong was returned to China. The declaration notes that Hong Kong’s “courts shall exercise judicial power independently and free from any interference.”

“The courts shall decide cases in accordance with the laws of the Hong Kong Special Administrative Region and may refer to precedents in other common law jurisdictions,” it adds.

The consequences of the latest assertion from the mainland remain to be seen, and what concrete actions Beijing may or may not take are unclear, though Zang hinted at possible legislative action.

“We are considering the relevant opinions and suggestions put forward by some NPC deputies,” he said, without elaborating.

Whatever the next step, it’s likely to only ratchet up tensions after months of protests that, ironically, were fueled by widespread fears of Beijing’s interference in Hong Kong’s affairs, particularly in the legal realm.

Meanwhile, Hong Kong author, lawyer, and commentator Antony Dapiran took to Twitter today to note the potentially dire impact of Zang’s statement.

“If this is a formal/official position, then this completely & fundamentally alters the landscape of the HK legal system and could quite legitimately be said to mean the end of the rule of law as we know it in HK,” he said.

CORRECTION: A previous version of this story incorrectly spelled the surname of the spokesman of the legislative affairs commission of the National People’s Congress standing committee. It is Zang, not Jian. Coconuts HK apologizes for any confusion.

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