Microsoft has told Windows 8 app developers that if they use the word "metro" in the name of their software, the app will be denied access to the Windows Store.
The warning now appears in online guidelines for developers, in a section labeled "Naming your app."
"Make sure your app name doesn't include the word metro," Microsoft cautioned. "Apps with a name that includes the word metro will fail certification and won't be listed in the Windows Store."
The ban on "metro" was first reported by the MarkedUp blog Tuesday.
Microsoft's move was the latest in its deprecation of the Metro label, one it had associated with Windows 8 for nearly a year, and used much longer with other products, including Zune and Windows Phone.
Last week, Microsoft confirmed it was dumping the Metro tag, but claimed that it had used it only as a code name. That held little water, however; The company had never said as much regarding Windows 8 or Windows RT, and in presentations, press releases and developer documents, the firm had repeatedly used the word to describe the apps and the WinRT-based environment they run in.
According to several reports, the name was ditched after Metro AG, a Dusseldorf, Germany-based conglomerate that's the world's fifth-largest retailer, complained.
Microsoft and Metro AG both declined to comment on the origin of the name change.
Also last week, websites such as The Verge and bloggers like ZDNet's Mary Jo Foley said their sources had said Microsoft was telling developers, partners and employees that Metro would be replaced by such phrases as "Windows 8 design" and "Modern UI."
As of Wednesday, there were still four free apps in the Windows Store that used the word "metro" in their titles, including "MetroTwit" and "Tweet Paint Metro."
It's unclear whether those apps' names will have to be changed, or if they will be "grandfathered" in under earlier rules.
On his blog iStartedSomething, Long Zheng, the developer of MetroTwit called the new restriction "illogical," and added that "We will be seeking legal advice."
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is firstname.lastname@example.org.