Chinese authorities have begun an anti-monopoly investigation into Alibaba, the country’s second largest private sector company. Alibaba has interests that range from e-commerce to cloud computing and movies.

State media announced on Thursday morning local time that the probe is being conducted by the State Administration for Market Regulation.

By the afternoon in Hong Kong Alibaba had put out a statement acknowledging the facts. “We have today received a notice of investigation (the “Notice”) from the State Administration for Market Regulation of the People’s Republic of China (the “SAMR”). The Notice states that the SAMR has commenced an investigation pursuant to the Anti-Monopoly Law of the People’s Republic of China. We will actively cooperate with the SAMR’s investigation. The Company’s business operations remain normal,” it said.

Only weeks earlier, the same regulator warned that it was concerned by the country’s tech giants. In the past week it followed that up by announcing fines for Alibaba and Tencent’s e-book and TV production offshoot China Literature for their conduct of corporate acquisitions.

Alibaba’s stock trades in ADR form in New York. Its shares are also traded via a secondary listing in Hong Kong. The reaction to news of the probe was swift. In early trading Thursday, the Hong Kong listed shares tumbled $5.6% to HK$234.40 apiece, down from an overnight close of HK$248.4.

Alibaba has also tangled with regulators in other areas in recent weeks. The $35 billion IPO of Alibaba’s financial affiliate Ant Group was halted in November, apparently after direct intervention by President Xi Jinping.

China’s financial watchdogs, including the central bank and insurance regulator, said they will hold talks with Ant Group in the next few days. On Thursday, Ant acknowledged that it has received a notice from regulators to attend a meeting. It said that it will strictly comply with all regulatory requirements.

In November, the State Administration for Market Regulation released draft rules that, for the first time, clearly define anti-competitive behavior. They appear to cover areas including pricing, payment methods, and use of data to target shoppers.

These points may be genuine concerns, but the massive scale of market leaders including Alibaba, Tencent, JD.com and Baidu, may also be seen as a challenge to the governance of the country.

Even though they already largely cooperate with the central government on matters such as censorship, China’s tech companies are now so large and multi-tentacled that they have the potential to represent another source of power and organization in Chinese society other than the Communist Party-led government.

The – until now—largely benevolent control of the Chinese tech sector has also allowed the Middle Kingdom tech companies to account for a far larger portion of the Chinese economy than their equivalents in North America and Europe, and to achieve massive profits.

Alibaba’s media and entertainment interests include: ownership of Youku, the country’s third largest video streaming company; Taopiaopiao, one half of a duopoly in the area of online movie ticket sales; UCWeb, a popular browser for mobile devices; and Alibaba Pictures, a sprawling movies operation that encompasses distribution and marketing, data services and production.

In recent weeks, Alibaba Pictures announced that it would henceforth focus more on film and TV series production than its previous strategy of becoming an industry platform. At the same time, it unveiled a massive slate of new productions. In the past week, it was announced that Alibaba would be allowed to pay nearly $1 billion for a small slice of state-backed streaming company Mango TV.

Alibaba Pictures also owns share stakes in companies including exhibitor Dadi, vertically-integrated studios Bona Film Group and Huayi Bros., and film financier Hehe Pictures.