While it seems like every company and its brother has jumped onto the mobile, streaming music train, there was a time when Pandora was king. And just like any other music service, the company has faced its share of hurdles when it comes to licensing with record labels. Today, Pandora has re-instituted a cap on its free, non-subscriber listeners.

As noted by TechCrunch, this isn't the first time Pandora has instituted a 40-hour monthly cap on free listening. The cap was lifted back in late 2011, but now it seems the limits are back on, and Pandora is blaming ongoing licensing issues.

"Most of you reading this will never hit the limit," wrote Pandora co-founder Tim Westergren on the company's blog. "In fact, it will affect less than 4-percent of our total monthly active listeners. For perspective, the average listener spends approximately 20 hours listening to Pandora across all devices in any given month."

Pandora claims the amount the company must pay per-track for royalties has increased by 25-percent over the last three years. The royalty rate is apparently expected to increase an additional 16-percent over the next two years. Granted, listening to Pandora without a subscription isn't exactly free: you're still subjected to ads.

The company blog states those approaching the 40-hour threshold will receive notification from Pandora. Ad-free, unlimited streaming is available for $3.99 via Pandora One.

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