Microsoft has been calling its distinctive tile-based user interface "Metro" since its first appearances on Windows Phone. But not any more-- since no other than Metro AG owns the "Metro" name.

According to anonymous sources speaking to Ars Technica, the German retailer is threatening Microsoft with legal action, causing the Microsoft Legal and Corporate Affairs team to send out a memo (also leaked to The Verge) banning use of the "Metro" name.

As we all know, Metro is huge, and a quick check through the German DPMA register reveals the retailer registered the "Metro" name for use in computer software, hardware and even storage devices.

In other words, Metro has a case against Microsoft should legal push comes to shove.

What shall we call the Microsoft tile-based, then? Very simply-- "Windows 8-style UI" when referring to Windows 8 applications and "New User Interface" when talking about all Microsoft products using the UI.

Ars Technica quotes a Microsoft spokesman saying "We have used 'Metro style' as a code name during the product development cycle across many of our product lines. As we get closer to launch and transition from industry dialog to a broad consumer dialog we will use our commercial names."

Interestingly, the press release announcing Office 2013 around 2 weeks ago does not refer to Metro-- it instead mentions "Windows 8-style applications for Office."

Go Microsoft: "Metro" Out, "Windows-Style UI" In (Ars Technica)

Go Microsoft's Metro Branding to be Replaced According to Internal Memo (The Verge)