China on Tuesday approved a contentious national security law for Hong Kong that takes direct aim at some of the actions of anti-government protesters last year, in a move many see as Beijing’s boldest yet to erase the legal firewall between the semi-autonomous territory and the mainland’s authoritarian Communist Party system.

Details of the law remained under wraps until 11 p.m. (1500 GMT, 11:00 a.m. EDT), when it was published and took effect immediately.

The text specifies that those who destroy government facilities and utilities would be considered subversive. Damaging public transportation facilities and arson would constitute acts of terrorism. Any person taking part in secessionist activities, whether organizing or participating, will violate the law regardless of whether violence is used.

“We hope the law will serve as a deterrent to prevent people from stirring up trouble,” said Tam Yiu-Chung, Hong Kong’s sole representative on the Standing Committee “Don’t let Hong Kong be used as a tool to split the country.”

The law took effect ahead an hour before July 1, the 23rd anniversary of the territory’s passing from Britain to China. Amid protests in Hong Kong last year, demonstrators broke into the legislative building on the anniversary, spray painted slogans on the walls and heavily damaged the electronic voting system.

During months of protests, they frequently smashed subway ticket machines and electronic sensors at entry gates, and disrupted service by holding doors open so trains couldn’t leave the stations.

President Xi Jinping signed a presidential order promulgating the law after its approval by the Standing Committee of the National People’s Congress, the official Xinhua News Agency said. It was to be added to the Basic Law, Hong Kong’s constitution.

Under the law, those found guilty of inciting secessionist, subversive, terrorist activities and colluding with foreign forces could face life imprisonment if they are deemed masterminds of such activities.

The legislation also states that Hong Kong’s government “shall take necessary measures to strengthen publicity, guidance, supervision and management” for schools, social groups, media, internet and other matters related to national security.

Hong Kong will establish a committee responsible for maintaining national security in the city. It will be chaired by chief executive Carrie Lam and will be accountable to and supervised by the Chinese government.

Passage of the law came amid fears in Hong Kong and abroad that it would be used to curb opposition voices in the financial hub. The U.S. has already begun moves to end special trade terms given to Hong Kong after the former British colony was returned to China in 1997.

Speaking in a video message to the U.N. Human Rights Council in Geneva, Lam said the law would “only target an extremely small minority” of lawbreakers, would not be retroactive, and that mainland legal bodies would only have jurisdiction in “rare, specified situations.”

Critics say it is the most significant erosion to date of Hong Kong’s British-style rule of law and the high degree of autonomy that Beijing promised Hong Kong would enjoy at least through 2047 under a “one country, two systems” framework.

Hong Kong pro-democracy activists Joshua Wong, Agnes Chow and Nathan Law issued statements on Facebook saying they would withdraw from their organization Demosisto, which then announced that it would disband with the loss of its top members.

Wong said “worrying about life and safety” has become a real issue and nobody will be able to predict the repercussions of the law, whether it is being extradited to China or facing long jail terms.

A group of about 30 pro-China supporters gathered at Hong Kong’s Tamar Park on Tuesday, waving Chinese flags. Organizers said that the rally was to show support of the national security law, and to celebrate Hong Kong’s return to China.

Meanwhile, more than 100 protesters gathered at a luxury mall in Hong Kong’s Central business district, chanting slogans including “Free Hong Kong, Revolution Now,” with several holding a flag representing an independent Hong Kong as well as posters condemning the law.

The law’s passage “represents the greatest threat to human rights in the city’s recent history,” said Joshua Rosenzweig, head of Amnesty International’s China Team.

“The speed and secrecy with which China has pushed through this legislation intensifies the fear that Beijing has calculatingly created a weapon of repression to be used against government critics, including people who are merely expressing their views or protesting peacefully,” Rosenzweig said in a statement.

Concerns also were expressed in Taiwan, which Beijing claims as its own territory to be brought under its control by force if necessary.

“Democracy and freedom are shared universal values of Hong Kong and Taiwan,” the island’s Mainland Affairs Council said, adding that China had betrayed its promises to Hong Kong,

The self-governing island recently said it would consider providing asylum for Hong Kong opposition figures who fear arrest.

Ahead of the law’s passage, the Trump administration said it will bar defense exports to Hong Kong and will soon require licenses for the sale of items that have both civilian and military uses.

“We cannot risk these items falling into the hands of the People’s Liberation Army, whose primary purpose is to uphold the dictatorship of the (ruling Communist Party) by any means necessary,” Secretary of State Mike Pompeo said in a statement.

British Foreign Secretary Dominic Raab said his government was “deeply concerned” by reports of the law’s passage, saying that would be a “grave step.” Britain has said it could offer residency and possible citizenship to about 3 million of Hong Kong’s 7.5 million people.

“This issue is purely China’s internal affairs, and no foreign country has the right to interfere,” Chinese foreign ministry spokesperson Zhao Lijian said.

He said China would take necessary measures to protect its national interests in response to “the wrong acts of the United States.”

Under the law, Beijing will set up a national security office in Hong Kong to collect and analyze intelligence and deal with criminal cases related to national security.

Government critics fear Beijing will use the law to pursue political opponents. Some have questioned the legal basis for the legislation, saying it undermines the Basic Law.

An earlier attempt to pass a security law in 2003 was dropped after hundreds of thousands of people marched in Hong Kong against it.

China for years had put off another such effort. Citing a new urgency after last year’s protests, it announced it would bypass the Hong Kong legislature and enact the law on its own.

Chinese officials have railed against what they call foreign interference in the territory that they blame for encouraging the anti-government protests. Beijing condemned the protests as an attempt to permanently split Hong Kong from China.

Drafting of the law took place amid intense secrecy, with even top Hong Kong officials reportedly not given advance notice of its specifics.

Questions linger over the effects on Hong Kong’s free press that has come under increasing political and financial pressure, as well as the operations of nongovernmental organizations, particularly those with foreign connections.

The law’s passage comes after Hong Kong’s legislature in early June approved a contentious bill making it illegal to insult the Chinese national anthem. Pro-China figures have also been pushing for more “patriotic” education to be introduced into the curriculum in hopes that will boost their identification with Beijing.