An apparent endorsement of Windows 10 by a top Defense Department official has a technology group crying foul.

In a letter sent to Defense Secretary Ashton Carter last month, the Software and Information Industry Association (SIIA) raised concerns after the Pentagon’s chief information officer, Terry Halvorsen, made comments, first highlighted by FedScoop, suggesting that employees not using Windows 10 at home were doing themselves an “injustice.”

In a conference call with reporters, Halvorsen praised the operating system’s security prowess, stating that the Defense Department has never had “an operating system that had this much security baked in from the beginning.”

“We’re going to put out some guidance to our employees in general—it’s not an endorsement of Windows 10 or Microsoft specifically—listing what the characteristics of Windows 10 would give you if you put it in your home system,” Halvorsen said in the conference call, according to FedScoop. “That’s as close to an endorsement as I can get for a software product.”

That was apparently too close for SIIA, which raised concerns with Halvorsen’s boss. Traditionally, the Department of Defense has not specifically endorsed any technology product, because such an endorsement could prove damaging in the marketplace. In the letter to Carter [PDF], SIIA President Ken Walsh highlighted the section of the DOD Joint Ethics Regulation that prevents the organization from making such an endorsement.

“These policies are very clear: endorsements by Federal officials of commercial products or services create an unfair advantage in the marketplace and, therefore, are prohibited,” Walsh wrote. “In this case, there is a very competitive market for personal computing operating systems, and Mr. Halvorsen cannot state his personal opinion about the merits of one product over another.”

SIIA added that Halvorsen failed to make it clear how he’d concluded that Windows 10 was better than other options, such as Linux or Apple’s OSX operating systems.

The Defense Department is currently working to upgrade its systems to Windows 10, a massive upgrade that affects roughly 4 million devices.

Regarding the letter, SIIA Senior Director of Public Policy David LeDuc noted that the approach seemed unprecedented, which prompted the group to speak out.

“This is a really unusual practice, something we can’t recall seeing, something we thought was inappropriate and unhelpful for the market, so we decided to weigh in and raise our concerns,” LeDuc told Nextgov last month.

(Shannon Stapleton/Reuters)