China is banning Windows 8 devices from at least some government IT purchases, in a mysterious move that took Microsoft off guard. The ban came from China’s Central Government Procurement Center, which posted a brief notice last Friday on new requirements for government tenders. Among the demands is that Windows 8 be excluded from the bidding process on computer purchases. It’s unclear how far-reaching the ban will be. The agency could not be reached Tuesday and the new requirements only concern government purchases for “energy-efficient” IT products, including notebooks, desktops and tablets.

China has banned government use of Windows 8, Microsoft Corp’s latest operating system (OS), in a blow to the U.S. technology company which has long been plagued by sales woes in the country. The Central Government Procurement Center issued the ban on installing Windows 8 on government computers as part of a notice on the use of energy-saving products, posted on its website last week. The official Xinhua news agency said the ban was to ensure computer security after Microsoft ended support for its Windows XP operating system, which was widely used in China. Neither the government nor Xinhua elaborated on how the ban supported the use of energy-saving products, or how it ensured security. China has long been a troublesome market for Microsoft. Former CEO Steve Ballmer reportedly told employees in 2011 that, because of piracy, Microsoft earned less revenue in China than in the Netherlands even though computer sales matched those of the U.S. Microsoft declined to comment.