China is giving Microsoft 20 days to explain “compatibility problems” with its Windows and Office software. China’s State Administration for Industry and Commerce (SAIC) posted the notice and demands that Microsoft offer a written explanation within the allotted time.

The Chinese regulator has yet to fully elaborate on the investigation’s specifics, but they have raided several company offices in China to obtain information on contracts, financial statements, and internal emails.

In May, a Chinese procurement center banned certain purchases of Windows 8. State-controlled media claimed the action was related to security concerns with the software.

Microsoft is not the only company China is investigating. Among them is Qualcomm, which has allegedly been overcharging clients to use its patents.