Alibaba Group Holding’s US-listed shares fell in the biggest one-day fall of all time amid concerns over China’s investigation into suspected monopoly practices at the e-commerce company.

Affiliate Ant Group Co., the other pillar of billionaire Jack Ma’s internet empire, was also invited to a high-level meeting on financial regulations.

The pressure on Ma is central to China’s broader efforts to contain an increasingly influential internet sphere: The draft antimonopoly rules released in November gave the government ample leeway to hold back entrepreneurs who, until recently, had unusual freedom to enter their areas expand.

The Alibaba investigation is “a warning the winds have shifted,” Bloomberg Intelligence said in a research report. According to analyst Vey-Sern Ling, there is a risk that business operations “can face long-term headwinds” as a result of such measures.

The stock fell 13% in its largest one-day decline in history. The decline brought Alibaba to its lowest level since July, and the stock is now 30% down from its October high. Around 141 million shares traded hands, most for a single session since debuting in 2014.

Alibaba said it will work with regulators in its investigation and its business will remain normal.

Alibaba and rivals like Tencent Holdings Ltd., once hailed as the drivers of economic prosperity and symbols of the country’s technological prowess, are facing increasing pressure from regulators after they have amassed hundreds of millions of users and affect almost every aspect of daily life have won in China.

“It is clearly an escalation in coordinated efforts to contain Jack Ma’s empire, symbolizing China’s new too big to fail” entities, “said Dong Ximiao, a researcher at the Zhongguancun Internet Finance Institute. “The Chinese authorities want a smaller, less dominant and more compliant company.”

China’s top antitrust watchdog, the state administration for market regulation, said in a statement it is investigating Alibaba but did not provide any further details.

Regulators, including the Central Bank and the Bank Guard, will separately invite subsidiary Ant to a meeting to bring home increasingly stringent financial regulations that are now a threat to the growth of the world’s largest online financial services company. Ant said in a statement that it will study and meet all requirements.

Ma, the flamboyant co-founder of Alibaba and Ant, has all but disappeared from the public eye since Ant’s IPO last month. In early December, the man most closely identified with the meteoric rise of China Inc. was advised by the government to stay in the country, said a person familiar with the matter.

Ma is not on the verge of personal doom, those familiar with the situation have said. Instead, his public reprimand is a warning that Beijing has lost patience with the overwhelming power of its technology moguls, increasingly seen as a threat to the political and financial stability that most praises President Xi Jinping.

Alibaba shares fell 8% in Hong Kong to a five-month low on Thursday. Asia’s largest company after Tencent has caused losses to China’s internet sector leaders since Ant’s IPO, bringing the total fee to around $ 200 billion. Shares of Tencent and internet service giant Meituan fell more than 2.6% at the end of the day, while shares of SoftBank Group Corp., Alibaba’s largest shareholder, fell 1.7% in Tokyo.

As China prepares for the introduction of the new antimonopoly regime, the country’s leaders have said little about how hard they are planning to contain or why they have decided to act now.

China’s internet ecosystem – long sheltered from competition from Google and Facebook – is dominated by two companies, Alibaba and Tencent, via a labyrinthine investment network that includes the vast majority of the country’s startups in areas such as artificial intelligence and digital finance .

Her patronage has also nurtured a new generation of titans, including food and travel giants Meituan and Didi Chuxing – China’s Uber. Those who thrive outside of orbit, with TikTok’s largest owner, ByteDance Ltd. is are rare.

The antimonopoly rules now threaten to disrupt that status quo with a range of potential outcomes, from a harmless fine scenario to breaking up industry leaders.

Some analysts predict there will be a tough crackdown, but a targeted one. They refer to the language in the regulations that suggests a strong focus on online trading, including enforced exclusive agreements with traders known as “Pick One of Two” and algorithmic pricing that new users prefer. The regulations explicitly warn against selling below cost in order to weed out competitors.

But Beijing agencies seem to be coordinating their efforts – a bad sign for the internet sector.

“There is nothing that the Chinese Communist Party does not control, and anything that seems to spin out of orbit in any way is being withdrawn very quickly,” said Alex Capri, a Singapore-based research fellow with the Hinrich Foundation.

The campaign against Alibaba and its colleagues was in full swing in November after Ma publicly accused Chinese regulators of being behind the times. The market regulators then suspended Ant’s largest IPO in the world at $ 35 billion, and the antimonopoly watchdog shook the markets shortly afterwards with his draft law.

The Volkszeitung, the mouthpiece of the Communist Party, warned on Thursday that the fight against alleged monopolies was now the top priority. “Antimonopoly has become an urgent matter of concern,” said a comment that coincided with the announcement of the investigation. “Wild growth” in the markets needs to be curbed by law, he added.

The chances of Ant resurrecting its massive public listing next year are diminishing as China overhauls rules for the fintech industry, which has been booming in recent years as an alternative to traditional government-sponsored lending.

China is said to have separately set up a joint task force to oversee Ant, led by the Financial Stability and Development Committee, a regulator for the financial system, as well as various departments of the central bank and other regulators. The group is in regular contact with Ant to gather data and other materials, investigate their restructuring, and draft other rules for the fintech industry.

“China has tightened much of its bureaucracy so that the various regulators can now more easily work together,” said Mark Tanner, general manager of the Shanghai-based consultancy China Skinny. “Of all the regulatory hurdles, this is by far the greatest.”