Earlier this month, Metallica’s entire catalog was made available on Spotify. It was a major grab for the European streaming service, with Metallica being one of the biggest and best-selling groups in rock (not just metal). But would the move prove to be a good one for Metallica? Well, new reports suggest that the move to Spotify may have had an effect on Metallica’s album sales…but not in a good way.

According to Billboard.biz, Metallica’s studio albums have supposedly taken a dip in sales since being made available via Spotify. Taking a look at Nielsen SoundScan data for Metallica’s studio albums for four-week periods leading up to Christmas from 2008 to 2012, Billboard.biz found that album sales were 15% below expectations the week the titles were added to Spotify, and 35% below expectations the following week. Plus, during the four-week period leading up to Christmas, Metallica’s sales increased to 27.2%. That pales in comparison to the 60% to 61% increase they experienced during the same time range in 2010 and 2011.

With that said, Billboard.biz does acknowledge that Spotify may not be entirely to blame. They do note that the end of the SoundScan sales week this year occurred further away from Christmas, while sales weeks ending closer to Christmas tend to better reflect late holiday shopping. It also doesn’t help that the number of retail outlets to purchase music has decreased dramatically over the years. Plus, it wouldn’t be hard to believe that Metallica’s agreement with Spotify includes a higher percentage of revenue from streaming.

Still, many continue to question whether Spotify actually helps or hurts existing album sales, and Metallica’s decreases in sales aren’t helping the streaming service’s case. Furthermore, this isn’t exactly a great start for Metallica own label.