The answer comes down to the Basic Law, the city’s mini-constitution, the scope of which the central government has increasingly defined in response to a surging localist movement calling for greater self-determination.

A Beijing insider said the top leadership could not stand by while the city’s basic ability to govern was at stake, and warned even further criticism might lie ahead, while a mainland legal expert cautioned the comments reflected a growing frustration over the pro-establishment camp’s failure to produce results even with a legislative majority.

The camp has 43 seats in the 70-member legislature versus 24 seats for the opposition, which has lost members over the past years to disqualification.

In the eyes of pro-democrats, the accusations by the cabinet-level Hong Kong and Macau Affairs Office (HKMAO) and the central government’s liaison office on Monday, that lawmakers had paralysed the Legislative Council with filibustering tactics, were yet another example of Beijing tightening its grip over the city’s political life.

As evidence, the liaison office pointed to a pile-up of bills and subsidiary legislation in the agenda-setting House Committee, leaderless since October. The affairs office suggested members had failed to carry out their duties, a charge that echoes the ousting of several opposition lawmakers for improperly taking their oaths in October 2016.

“One can’t help thinking their behaviour amounts to a breach of the [Legislative Council] oath, and constitutes an offence of misconduct in public office,” the HKMAO said.

Legal sector lawmaker Dennis Kwok of the Civic Party, as de facto head of the committee who has been presiding of the meetings, fired back that Beijing’s representatives were themselves guilty of crossing an inviolable line.

“I’d like to remind the [central government] agencies that under the ‘one country, two systems’ policy, no mainland units can interfere with Hong Kong’s internal affairs,” Kwok said.

Chief Executive Carrie Lam Cheng Yuet-ngor threw her support behind Beijing on Tuesday, arguing the offices had every right to criticise the lawmakers. “When the Legislative Council is almost malfunctioning … I find it only legitimate for them to express concern,” Lam said. But she refused to say if the government would move to unseat the lawmakers and instead asked the legislature to resolve the impasse.

The criticisms by the offices were a foray into a sphere of city life where the central government rarely treads. Under Article 2 of the Basic Law, China’s legislature, the National People’s Congress (NPC), authorises Hong Kong to exercise a high degree of autonomy and enjoy executive, legislative and independent judicial power. But that privilege ends where matters of defence or foreign affairs are concerned.

In the first years after the 1997 handover from Britain, Beijing refrained from overtly commenting on Hong Kong governance, confident the city could run itself. That stance changed after July 1, 2003, when 500,000 residents took to the streets to protest against proposed national security laws, which the legislature is required to pass under the Basic Law but are widely seen as a precursor to muffling dissent.

The next January the affairs office issued an unprecedented statement on the policy address delivered by then chief executive Tung Chee-hwa. It was the first time since the handover that Beijing had commented formally on the biggest government announcement of the year. That April, the central government took its largest step into local politics yet with an interpretation of the Basic Law that ruled out the election of the chief executive and all Legco members, some of whom are industry appointed, by universal suffrage for 2007 and 2008, despite Beijing’s earlier promises.

That was followed by a State Council white paper in June 2014 that pointed to the central government’s “comprehensive jurisdiction” over the city and stressed that Hong Kong’s high degree of autonomy was subject to Beijing’s authorisation.

The acts that got six Hong Kong lawmakers disqualified

The top leaders drew a line in the sand again in 2016 after six pro-democracy politicians elected to Legco used their oath-taking ceremony to mock the mainland with various antics. Then justice secretary Rimsky Yuen Kwok-keung launched a judicial review that led to the NPC interpreting Article 104 of the Basic Law as requiring lawmakers to be “sincere” in taking their pledges or face disqualification. Violators “shall bear legal responsibility”, it said.

“What Dennis Kwok and other opposition lawmakers have been doing since October has obviously breached Article 104 of the Basic Law and the interpretation by the NPC Standing Committee in 2016,” said Tam Yiu-chung, Hong Kong’s sole representative to the standing committee, the nation’s top legislative body. Tam said the boundaries laid down under one country, two systems must not be understood in the narrow sense that the central government could only state its position on matters such as national defence or political reform.

A source familiar with Beijing’s position agreed. “The central government can’t turn a blind eye to the chaos in Legco, which has already undermined the prosperity and stability of Hong Kong,” the insider said. “It wouldn’t be a surprise to see the central government agencies speak up on other issues affecting Hong Kong’s fundamental interests in the days ahead.”

Tian Feilong, an associate professor at Beihang University’s law school in Beijing, said the central government’s patience was wearing thin, but the offices’ criticism also targeted the pro-establishment camp for failing to put Legco in order.

“It’s a reminder from the central government to the pro-establishment camp that it has not been exercising its legitimate power to ensure the smooth operation of the legislature,” Tian said.

The bills held up in committee involve policy areas ranging from hotel regulation and fire services to the city’s competitiveness and an extension of maternity leave. But a national anthem bill, which defines how people must behave when March of the Volunteers is played in Hong Kong, is widely viewed as the Rubicon. “The disruption of the national anthem bill is another example of disrespect for national sovereignty,” the mainland source said.

Lau Siu-kai, vice-president of semi-official think tank the Chinese Association of Hong Kong and Macau Studies, said the central government believed the city was at a crisis point as the United States stepped up support heading into America’s critical election cycle after a globally disruptive trade war still far from settled. The administration of Donald Trump was playing the anti-China card, he said, with the city as a pawn.

“Beijing also notes that the opposition has turned radical and it cannot persuade them to be less confrontational,” he said.

Beijing would not sit idly by while the US plotted strategies for the balance of power to be decided at September’s Legco election, Lau said.

Both pan-democrats and the pro-establishment camp are gearing up for what is expected to be a decisive campaign battle due in September, after months of unrest sparked by the administration’s failed attempt to introduce an extradition bill and the opposition’s landslide victory in November’s local council elections. The fear is that the opposition could make big inroads in the legislature, upending the dominance of the pro-establishment camp and making it even harder for the government to pass bills.

Pro-Beijingers believe the warnings are clearly related to the upcoming poll. Referring to the opposition, Horace Cheung Kwok-kwan of the pro-government Democratic Alliance for the Betterment and Progress of Hong Kong, said: “They uphold the ‘if we burn, you burn with us’ mentality since the protests against the extradition bill. The pan-democrats openly said that if they gain the majority, they will veto all government bills and funding. It is their intention to paralyse Legco, and even the government.”