The major record companies may not be playing sweet music to consumers when it comes to digital downloads, as the US Department of Justice has launched an investigation into leading music online pricing policies.

The four largest music companies - EMI, Sony BMG, Warner Music and Universal Music Group are to be reviewed to ensure no naughty pricing practices are in place.

A spokeswoman for the department said: "The anti-trust division is looking at the possibility of anti-competitive practices in the music download industry."

Although legal digital downloads tripled last year to $US1.1 billion ($1.47 billion), and account for about 6 per cent of the industry's revenues, they have still failed to offset the continued decline in sales of CDs and the ravages of piracy.

Pricing has been a matter of contention in the fledgling digital market.

Under an agreement with Apple, whose iTunes store controls 80 per cent of the online music market, customers are charged US99c a track. Of that amount, record companies pocket about two-thirds.