Lyrics sites are the latest in the crosshairs of the National Music Publishers' Association, an organization set up to protect the copyrights of songwriters.
The NMPA sent take-down notices citing the Digital Millennium Copyright Act to the biggest 50 lyrics Web sites that it said profit from advertising without compensating songwriters.
"This is not a campaign against personal blogs, fan sites, or the many websites that provide lyrics legally," NMPA president and CEO David Israelite said. "NMPA is targeting 50 sites that engage in blatant illegal behavior."
The take-down notices tell a recipient that its site displays lyrics of thousands of copyrighted musical compositions and that substantially all the lyrics are unlicensed. Unless it ceases the violations, the NMPA said it would continue to send take-down notices and would contact the site's Internet service provider and search engines, which could result in the site being removed completely.
CNET has reached out to a handful of the biggest sites on the the list that the NMPA based its campaign on -- those found by University of Georgia's researcher David Lowery. We will update this report when we hear back.
Rap Genius founder Ilan Zechory, who's site made Lowery's list, said that he hasn't heard anything from the NMPA yet, but that he "can't wait to have a conversation with them about how all writers can participate in and benefit from the Rap Genius knowledge project." In an email to CNET, Zechory called the project much more than a lyrics site.
Lowery's research listed Rap Genius as the site with the highest "score" when measuring how often and how high sites are returned in search results for a song title, artist name, and popular lyrics snippet.
Earlier this year, the NMPA sued Fullscreen, one of the biggest so-called "multichannel networks" on YouTube. Another -- Maker Studios -- settled a similar complaint.