Amazon received a “blistering” letter last Thursday about copyright infringement and Twitch’s nonexistent licensing deals with major music rights holders, Variety reports. The letter was signed by organizations including the Recording Industry Association of America (RIAA), the Recording Academy, the National Music Publishers Association, the American Association of Independent Music, SAG-AFTRA, and more.

The document accuses Twitch of allowing streamers to play copyrighted music without getting the proper licensing to do so. (Music copyright is a thorny, complicated subject; if you want to play music to audiovisual content, you need at least two different licenses to do it legally: a synchronization license and a mechanical license.) “Twitch appears to do nothing in response to the thousands of notices of music infringement that it has received nor does it currently even acknowledge that it received them, as it has done in the past,” the letter reads in part, according to Variety.

About a week ago, Twitch sent out a notice informing thousands of streamers that they had infringed copyright and that the platform was deleting the offending videos. The letter to Amazon appears to be the next step by the RIAA in a campaign to make a case that Twitch isn’t abiding by the terms of the Digital Millennium Copyright Act, which governs copyright online. That could open it up to be sued for copyright claims. There is a precedent for this: media companies sued YouTube between 2007 and 2009 on the same grounds, which led to the creation of a content fingerprinting system the company still uses to root out copyright infringement.

On YouTube, rights holders can now collect the ad revenue on a copyrighted video, if they so choose, and can take infringing channels down. The legal wrangling over licenses suggests the RIAA is angling for something similar with Twitch.

The letter also blasted Twitch’s new Soundtrack tool, which separates music from the audiovisual stream and strips it out of archived broadcasts. The groups that sent the letter say they’re “confounded by Twitch’s apparent stance that neither synch nor mechanical licenses are necessary for its Soundtrack tool.”

In response, Twitch provided Variety with a statement that contends that the company is supporting the music economy by paying royalties to performing rights organizations — the publishing side of the music business. That means Twitch is paying for licenses, just not the ones the RIAA wants. Public performance licenses, which is what Twitch is paying for, allow places like restaurants to play music in public. Twitch also said that its Soundtrack feature is fully licensed and that it had agreements in place with rights holders for the music featured in the product.

The industry groups say they’re concerned that unlicensed music is still widely available on Twitch, despite its claims that the company would remove it: “Twitch appears to do nothing in response to the thousands of notices of music infringement that it has received nor does it currently even acknowledge that it received them.”