Music streaming firm Spotify AB is being sued for a massive $1.6 billion by Wixen Music Publishing, even as it reportedly made a confidential filing for an initial public offering.

The IPO filing, according to Axios, could happen in the first quarter. But the suit by Wixen, which handles more than 2,000 clients that include The Doors, Janis Joplin, Neil Young, Tom Petty, The Beach Buys, Weezer and The Black Keys, could affect that timing.

The lawsuit, filed Dec. 29 in a California federal court, alleges that Spotify is using tens of thousands of songs without a license to do so. Those songs include classics such as Tom Petty’s “Free Fallin’” and the Doors’ “Light My Fire,” according to reports.

“Prior to launching in the United States, Spotify attempted to license sound recordings by working with record labels but, in a race to be first to market, made insufficient efforts to collect the required musical composition information,” read the complaint. It added that Spotify had “failed in many cases to license the compositions embodied within each recording or comply with the requirements of Section 115 of the Copyright Act.”

Spotify has found itself on the wrong end of a slew of lawsuits of late. In May, the company proposed a $43 million settlement in a class action copyright lawsuit when it was accused of distributing copyrighted songs and not paying the toll for mechanical licenses.

Following that, Spotify was accused of not doing enough to ensure artists and publishers get their cut when songs are streamed, while the settlement was deemed by many artists as being paltry. More lawsuits ensued.

Section 115 of the Copyright Act requires that if a company reproduces a song, such as Spotify’s streaming someone’s music, it can do so without negotiating terms with the artist and publisher. The licensing rate is set by law. But it does require that a company sends a “notice of intention” or just makes the required payments. The lawsuits say that Spotify hasn’t done this in many cases.

According to reports, Spotify has said that when dealing with tens of millions of songs, finding writers and co-writers of musical compositions can be an almost impossible task. Critics of the service as well as lawyers have countered, saying that Spotify has made little attempt to pay its dues and that artists and publishers should not have to go to great lengths to be paid for their music.

Image: Philip Wilson via Flickr