Hardcore mobile listeners unwillingly to pay monthly may be upset to learn Pandora has announced that it will begin limiting free mobile listening to 40 hours a month. 

According to US-based Pandora, the change will affect only 4 per cent of its total monthly users, as the average listener usually listens to roughly 20 hours. It made the change to help pad a per-track royalty rate that will increase 16 per cent over the next two years.

"After a close look at our overall listening, a 40-hour-per-month mobile listening limit allows us to manage these escalating costs with minimal listener disruption," the company said in a blog post. 

Before the change, users were able to listen to music unlimitedly on Pandora's apps, of course dealing with ads as well. It's worth noting that the new limit will not affect desktop listening - only mobile. Pandora is available in the United States, Australia, and New Zealand. 

Users who wants to exceed the limit but doesn't want to pay for a membership can pay a $0.99 fee to continue listening. 

Competitor Slacker offers free unlimited listening.