Beijing has launched an antitrust investigation into ecommerce titan Alibaba as part of a crackdown on monopolistic behaviour in China’s booming online market.

Regulators had previously warned Alibaba about the so-called “choosing one from two” practice, under which sellers are required to sign exclusive deals preventing them from selling goods through other marketplaces.

China’s State Administration for Market Regulation (SAMR) said on Thursday it has now launched an official investigation.

Financial regulators will also summon representatives from Alibaba’s fintech affiliate, Ant Group, in the coming days. They said that meeting would be designed “to implement financial supervision, fair competition and protect the legitimate rights and interests of consumers”.

Both Ant and Alibaba said they would co-operate with the investigation.

It comes a month after China dramatically suspended Ant’s planned $37bn IPO just 48 hours before its shares were due to start trading in Shanghai and Hong Kong.

People’s Daily, the media outlet controlled by China’s ruling Communist Party, said that if “monopoly is tolerated, and companies are allowed to expand in a disorderly and barbarian manner, the industry won’t develop in a healthy and sustainable way”.

Shares in Alibaba tumbled almost 9% in Hong Kong on Thursday morning.

Fred Hu, chair of Ant Group investor Primavera Capital Group, told Al Jazeera that global markets would be interested to see whether China’s moves are “politically motivated or genuine impartial law enforcement”.

“It would be a tragedy if the antitrust law should be seen as ‘targeting’ successful private tech companies only,” he added.

China made its first major antitrust move against online players last month when it issued draft rules aimed at preventing monopolistic behaviour.

At the time, it warned the likes of Alibaba and its rivals and Pinduoduo to be prepared for increased scrutiny. The state also revealed plans to investigate mergers involving Alibaba and Tencent.

People’s Daily said that a monopoly “distorts allocation of resources, harms the interest of market players and consumers, and kills technological advancement”, adding that “fair competition is the core of the market economy”.