China has banned the use of Microsoft's latest operating system on government computers.
Beijing issued the restriction as part of a decree about the use of energy-saving products.
But official news agency Xinhua said security concerns related to foreign operating systems had led to the move.
Microsoft said it was surprised, but insisted it would continue to provide older versions of its software to the Chinese authorities.
Xinhua said Beijing had felt compelled to act after Microsoft ended security support for its Windows XP operating system, which is still widely used in China.
"The Chinese government obviously cannot ignore the risks of running OS without guaranteed technical support," it reported.
"It has moved to avoid the awkwardness of being confronted with a similar situation again in future if it continues to purchase computers with foreign OS."
A Microsoft spokesman said the government's procurement department had posted a notification online barring Windows 8 from bidding for public sector deals.
The spokesman said: "We were surprised to learn about the reference to Windows 8 in this notice.
"Microsoft has been working proactively with the Central Government Procurement Centre and other government agencies through the evaluation process to ensure that our products and services meet all government procurement requirements.
"We have been and will continue to provide Windows 7 to government customers. At the same time we are working on the Window 8 evaluation with relevant government agencies."
Xinhua reported that the ban covered all desktops, laptops and tablet PCs purchased by central state bodies. The measure only targets computers used by government offices, while the personal computer market is expected to stay unaffected, the agency reported.
The news agency suggested it could prove to be an opportunity for local Linux-based alternatives - including Kylin and StartOS - to gain ground.
"China's decision to ban Windows 8 from public procurement hampers Microsoft's push of the OS to replace XP, which makes up 50% of China's desktop market," said data firm Canalys.
Former Microsoft chief executive Steve Ballmer reportedly told employees in 2011 that, because of piracy, the firm earned less revenue in China than in the Netherlands, even though demand matched that of the US.
Microsoft ended support for the 13-year-old Windows XP last month in a bid to encourage the adoption of newer, more secure versions of Windows.
This has potentially left XP users more vulnerable to viruses and hacking.