Lyric sites are among the most popular on the web, helping people identify the name of a song or understand what a singer is saying. But many of these may be wiped off the web soon since the National Music Publishers Association has reportedly begun its battle to take down sites that do not have the rights to post these and profit from them.

According to Billboard, the NMPA has sent shut down notices to 50 sites that University of Georgia researcher David Lowery listed in a report last month as sites that likely do not have the rights to post these lyrics.

This list also includes the very popular RapGenius, which MTV News notes, has earned support from artists like Nas, who is the site’s first “Verified Rapper.”

Rap Genius Co-Founder Ilan Zechory told Billboard that he hasn’t heard anything from the NMPA. However, he said, “...we can't wait to have a conversation with them about how all writers can participate in and benefit from the Rap Genius knowledge project.”

Zechory added that his site features much more than lyrics and that it is different from other sites in the report, many of which just publish lyrics. “Rap Genius is an interactive encyclopedia for annotation of all texts - anyone can upload and annotate texts relating to music, news, literature, religion, science, their personal lives, or anything else they want,” he explained.

The New York Times reports that the NMPA noted that these sites have been profiting off of lyrics through ad sales, even though they have not gone through the proper channels to distribute them.

“These lyric sites have ignored the law and profited off the songwriters’ creative works, and N.M.P.A. will not allow this to continue,” NMPA president David Israelite said. He said that there is no crusade against sites that are legally publishing lyrics online, but the group is “targeting 50 sites that engage in blatant illegal behavior, which significantly impacts songwriters’ ability to make a living.”

Israelite noted that the shut-down notices are just the first step. The next will be filing copyright infringement lawsuits.

To see the full list of 50 sites the NMPA is targeting, here is Lowry’s full report.