By Ian Youngs
Music reporter, BBC News
Spotify has seven million users in six European countries
A group of songwriters have criticised the deals done to get their music on streaming services like Spotify.
The British Academy of Songwriters, Composers and Authors (Basca) said such services only generate "tiny" payments.
And its members cannot find out whether they should be getting more because the deals with record labels and publishers are kept secret, it said.
Spotify declined to comment but has said payments are rising as subscriber numbers and ad revenues increase.
Spotify has been a hit with fans by offering millions of tracks to stream online for free, with ads, or a premium offering for £9.99 a month.
But there has been uncertainty over whether such streaming services can make enough money to satisfy artists, writers, labels and other rights holders.
Basca chairman Patrick Rackow said songwriters want to support services like Spotify as they grow and start to turn a profit, but that there should be more openness with those who create the music.
"At the moment, the amounts of money that are actually being received are tiny," he said. "That might be because there is no money there.
"But there is no clear trail that can be established so that the songwriter can trace back what they ought to have got. These things are behind a blanket of secrecy, and that is extremely worrying.
"The danger is that these deals all become so secret that the mist that descends creates uncertainty, creates fear. That allied to the fact that the sums being paid through are very small creates a climate of suspicion.
"I think that harms Spotify, it harms the writers' perception of Spotify and this is a service that they want to support."
Record labels own a share of Spotify and Mr Rackow said the returns on that equity were "unlikely to filter down into payments for the artists".
"It is pretty tough for the averagely successful songwriter to make a living. It is much tougher than it used to be," he said.
"It's hard to say that anyone has a right to make a living out of writing songs but if you write songs that people actually want to hear then I think that does give you some sort of right to get some remuneration back."
Basca has about 2,000 members and organises the annual Ivor Novello songwriting awards.
Speaking to BBC News in January, Spotify boss Daniel Ek said: "The truth is that the amount of money an artist makes per stream is increasing because we're getting more and more people to become subscribers, our advertising revenue is growing month-on-month."
The BPI, which represents UK record labels, declined to comment, as did PRS For Music, which collects royalties on behalf of songwriters.