Sources have told CNET that the U. S. Department of Justice is in the preliminary stages of an investigation of Apple for antitrust issues.

CNET reported on Thursday that it is unclear whether a formal investigation will develop, but sources said DOJ officials have interviewed music executive from four major companies to see if Apple's dominance in digital music sales includes the company unfairly trying to squelch competition.

70 percent of the digital song market is now controled by Apple through iTunes. In addition, Apple sold 28 percent of all music sold in the first quarter in the United States, up from 19 percent two years ago.

It was also reported that an antitrust investigation is likely to include questions of Apple's response to Amazon. com's "MP3 Daily Deal," a promotion of individual songs that are put on sale the day of their release.

Billboard magazine, in April, published a story that said Apple told music labels it would refuse to run promotions on any music included in the MP3 Daily Deal. (With Inputs from Agencies)