Microsoft has started to notify its Windows developers that they should refrain from using the word "Metro" throughout their applications if they refer to the Windows Phone or Windows 8 interface. Instead, the company is advising developers to use "New User Interface" to describe Microsoft's unified design. One source, who wishes to remain anonymous, tells us that the change could be related to a dispute between Microsoft and a German company over the use of the Metro naming. Developers have been informed that they shouldn't use the term any more in apps or associated documentation.

We reached out to German company Metro AG, who say that they "do not comment on market rumours," neither confirming or denying a potential dispute over the Metro trademark they hold in Germany. Microsoft company officials confirmed to us that they're dropping the "Metro style" naming of Windows 8 apps. "We have used Metro style as a code name during the product development cycle across many of our product lines," says a Microsoft spokesperson. "As we get closer to launch and transition from industry dialog to a broad consumer dialog we will use our commercial names." Microsoft refused to comment on whether the move away from Metro naming is related to any potential trademark dispute.

Microsoft has been using Metro as an internal codename for its typography-based design language. Elements of the Metro principles were present in the company's Zune product and played a big role in Windows Phone 7. Microsoft currently refers to the new style of Windows 8 apps as Metro style ones, although that appears to be something they're planning to drop.

Update: Mary Jo Foley at ZDNet is also reporting on a "possible copyright dispute with some other entity."

Update 2: Microsoft is planning to name its Metro replacement this week, according to an internal memo.