Lu Zhenwang, chief executive officer of the Shanghai-based Wanqing Consultancy, said: "We can't decide whether Alibaba's behavior has broken the law, as it has its own promotional resources and has the right to allocate those resources to the retailers that support it."

Feng Xiaoqing, a professor from China University of Political Science and Law, however, said that Alibaba's "choose-one-side" approach "might have an effect on market competition".

"Tmall occupies a large share of the e-commerce sector, and any policy that requires retailers to choose one side or the other may be unfair to rivals."

According to a regulation issued by the State Administration of Industry and Commerce, e-commerce platforms should not "limit or exclude retailers that engage in promotional activities on its platform, to attend campaigns organized on third-party trading platforms". The regulation has been in effect since Oct 1.

"We should wait for the industry authority to decide whether Alibaba's behavior is permitted by law," Feng said.