China’s market regulator said Thursday that it had opened an anti-monopoly investigation into e-commerce giant Alibaba, ratcheting up the government’s scrutiny of one of the world’s most valuable internet companies.

In a terse statement, the State Administration for Market Regulation said it had started the investigation amid reports that Alibaba had engaged in monopolistic conduct such as placing unreasonable restrictions on merchants or other users of its platforms.

Representatives for Alibaba, which is based in the Chinese city of Hangzhou, did not immediately respond to requests for comment.

The investigation is part of a broader official pushback against the business empire of Jack Ma, Alibaba’s co-founder and by some counts China’s richest man.

In November, the market regulator released proposed rules aimed at combating anti-competitive behaviour at internet companies. Earlier that month, Chinese regulators halted the initial public offering of Ant Group, Alibaba’s finance-focused sister company, quashing a listing that had been on course to be the largest in history. The move came after Ma publicly criticized Chinese regulators for being too obsessed with containing financial risk.