Spotify is to cut back the amount of free listening available to users from 20 hours to 10.

From 1 May, the music streaming service will reduce by half the amount of free music available each month to its 6 million users in the UK and Europe.

Non-subscribers will only be allowed to listen to an individual track a maximum of five times. Users will move to the restricted model six months after they register – some existing users' listening time will remain free, for others the restricted plan starts on 1 May.

Since its 2008 launch, Spotify's free offering has become popular, tempting more than 1 million people to become paying customers.

"The service become incredibly popular. People are listening to more music and from a wider range of artists … and are giving up on piracy," Daniel Ek, Spotify's co-founder, announced in a blogpost on the company's website on Thursday. "This is exactly what we hoped would happen.

"So it's vital that we continue offering an on-demand free service to you and millions more like you," he added. "But to make that possible we have to put some limits in place going forward."

Ek said that the changes would mainly affect heavier users, and that people would still be able to listen to about 200 tracks, or 20 albums, free each month.

The move will no doubt rankle with some music fans, who had grown used to Spotify's free streaming service being "too good to be true". The first commenter on Spotify's official blogpost lamented: "So long Spotify. It was nice knowing you. Guess I'll go back to pirating music again then."

However, Ek told the Financial Times last month: "We are trying to experiment with new ways to increase monetisation on free as well as paid. We are constantly trying to get people to pay but we prefer using carrots rather than sticks."

The Anglo-Swedish company has been negotiating with the four major music labels – Universal, Warner Music, Sony and EMI – about its plans for a launch in the US. The music majors have long been wary of free music streaming services, like Spotify's non-premium offering.

Spotify has always insisted that a sizeable base of free users would eventually translate into paying subscribers. Last month, the company announced its 1 millionth paying customer – paying subscribers make up 15% of Spotify's active users.

The most recent audited annual accounts for Spotify, for 2009, show it lost £16.6m in the UK on revenues of £11.3m.