US authorities have ordered Warner Music to give evidence to an investigation into the price of digital music downloads.
Apple boss Steve Jobs has called record companies "greedy"
Warner said it was "co-operating fully" with the investigation by New York Attorney General Eliot Spitzer.
The US music industry has been criticised recently for considering increasing the cost of digital music.
The New York Attorney General's Office was not available to comment on the nature or scope of the investigation.
The amount consumers have to pay for music downloads has been a matter of fierce debate.
On Apple's iTunes service, US consumers pay 99 cents (57 pence) for each track. But record labels have indicated that they want to charge differing sums for each song.
In September, Warner chief executive Edgar Bronfman told investors that "not all songs are created equal".
"There are some songs for which consumers would be willing to pay more and some we'd be willing to sell for less," he said.
But Apple chief executive Steve Jobs has called the music industry's stance "greedy", warning any price hike could drive consumers to piracy.
Last month, Warner agreed to pay $5 million (£2.88m) to settle a separate probe into "pay-to-play" practices. The company had been accused of giving radio stations incentives to play songs.
Sony BMG paid $10 million (£5.77m) in connection with the same investigation, while Universal and EMI have not yet settled.