Google has sent Microsoft a cease and desist letter over the YouTube app Microsoft built for Windows Phone. According to a letter obtained by Wired, Google demands that Microsoft immediately remove the YouTube app from the Windows Phone Store and then disable the app on all existing handsets by May 22.

In its letter to Microsoft, Google claims that the YouTube app allows users to download videos and strip out ads. Here’s part of the letter from YouTube’s Director of Platform Partnerships:

“We recently became aware of a Microsoft-­authored YouTube application for Windows Phone 8 available at https://www.windowsphone.com/en­us/store/app/youtube/dcbb1ac6­a89a­df11­a490­00237de2db9e. It appears that the application: (1) allows users to download videos from YouTube; (2) prevents the display of advertisements in YouTube video playbacks; and (3) plays videos that our partners have restricted from playback on certain platforms (e.g., mobile devices with limited feature sets). These features directly harm our content creators and clearly violate our Terms of Service. We request that you immediately withdraw this application from the Windows Phone Store and disable existing downloads of the application by Wednesday, May 22, 2013.”

The YouTube app issue isn’t the only dust up Microsoft and Google have had today. During his Q&A at Google I/O this morning, Google CEO Larry Page mentioned that he was disappointed Microsoft integrated gChat into Outlook, without allowing Google and other companies to connect to Microsoft’s messaging service.

Neither company has commented on the cease and desist letter at this time. The two page letter can be read in its entirety over at Wired.

• SourceWired