China’s State Administration for Industry and Commerce (SAIC) has given Microsoft 20 days to answer questions about the compatibility of its Windows and Office software as part of an ongoing anti-monopoly investigation.

The company’s VP David Chen was questioned yesterday by the market regulator, which has accused the company of not fully disclosing issues about the compatibility of its OS and Office suite, Reuters said.

Microsoft’s use of verification codes “may have violated China’s anti-monopoly law”, Xinhua reported Monday. The codes, which come with legal software and are required for updates and support, are used by software companies to fight piracy.

The Chinese government, citing security concerns, issued a ban in May on Windows 8 in government offices.

An unnamed source for Sina news claimed that Microsoft’s problems in China have less to do with government surveillance or backdoors and more to do with its decision to stop supporting Windows XP, which is the most popular computer OS in China, Network World reported.

Microsoft and more than 30 other foreign tech companies are under investigation by China’s antitrust authorities, which have stepped up their efforts since early 2013. Some attribute the increase in cases to the growing maturity of the regulators, which have gained experience since the Chinese anti-monopoly law was passed in 2008. But others point to increasing concerns of protectionism, with the law used to favour domestic firms over foreign ones.

The country’s head of an anti-monopoly agency was quick to respond to such criticism.

Xu Kunlin, director of the bureau of price supervision and anti-monopoly of the National Development and Reform Commission, said domestic and foreign companies in China should review their operations to see if their practices fully abide by the anti-monopoly law, the official news agency reported today.

“Some business operators in China have failed to adjust their practices in accordance with the anti-monopoly law. Others have a clear understanding of the law, but they take the chance that they may escape punishment,” he told Xinhau.

US-based Qualcomm, facing its own probe, said last month it is willing to modify its pricing in China to put an end to an antitrust investigation by the National Development and Reform Commission (NDRC).

A Qualcomm delegation, which included President Derek Aberle, met with NDRC officials on 21 August.

Microsoft CEO Satya Nadella is expected to visit China for the first time this month – a trip that was reportedly planned before the latest developments.