Spotify will no longer be free.

We know: it’s the worst headline you’ve read all week. But it’s true: Spotify is pulling the rug out from under its free listeners.

Six months ago, the music streaming service made its US debut and quickly gained traction as the Internet’s preferred streaming / discovery service du jour, dwarfing contributions from other players like Pandora, MOG and Rdio. But that may change when the service hits its half-year anniversary this week. That’s when most free users will discover their previously unlimited, ad-supported listening privileges will be replaced with a 10-hour per month limit on free streaming (including a 5-play limit on any single song in Spotify’s archives).

Why the change? BBC News speculates Spotify is under pressure from record labels who see next to nothing in streaming revenue from free users (who comprise 85% of the site’s user base). Labels may be getting antsy that they’ve freely distributed their catalogues through Spotify and seen very little in return.

The service will begin at $4.99/mo for desktop streaming and $9.99/mo for mobile access. New users will still be treated to six months of unlimited streaming, though as we’re finding out now, there’s a pretty harsh comedown when the free music high ends.

Spotify built its reputation on free streaming, and users will be miffed at the sudden change. It’ll be interesting to keep an eye on Spotify’s competitors after the bait and switch. Both Rdio and MOG restructured their free streaming models to keep up with Spotify after its US debut. Now that Spotify has done an about-face on its core principle, jeopardizing its brand loyalty in the process. MOG, Rdio and others will have the opportunity to adapt and welcome any potential exodus from Spotify’s halls.

Tell us: will you still use Spotify when it imposes these new restrictions next week?