Google is in the process of contacting multiple websites that are used by millions to convert YouTube videos into MP3s. The search giant claims that such services are in violation of YouTube's terms of service and is giving site owners seven days to cease their practices or face potential legal consequences.

Sites like and allow a user to plug in a YouTube URL and within a few minutes, an MP3 of the audio from the video is made available for download. Services like this are immensely popular, especially among youth. receives 1.3 million visitors each day according to Google's DoubleClick service.

In the letter to site owners, YouTube's associate product counsel Harris Cohen notes that their ToS agreement prohibits applications that separate, isolate or modify audio or video components of any YouTube content made available through the site's API. Furthermore, it's illegal for any application to facilitate storing copies of YouTube content outside of the site.

In the interim, Google has reportedly blocked all of YouTube-MP3's servers from accessing YouTube, effectively rendering the site useless to visitors looking to create and download free music. For their part, YouTube-MP3 claims his site doesn't use the YouTube API but operates through different means.

It's unclear why Google is just now taking action against such sites and their practices but perhaps content creators like major record labels have been putting pressure on Google to mount an offensive. Just last year a group of record labels sued a similar racket called TubeFire.