Grainge was adamant that UMG is committed to expanding the digital channel, noting that the label has signed more than 100 partnerships with online music ventures in the United States, and hundreds more globally. Any effort to foreclose on digital distribution would amount to "commercial suicide," he said.

"From my experience and where I sit, we would be insane not to license, develop, make our music available through as many platforms, through as many retailers, as possible," Grainge said.

But skeptics of the transaction, including subcommittee chairman Herb Kohl (D-Wis.), raised concerns about the share of the market for music sales the combined entity would wield, which by some estimates would be more than 40 percent. For Kohl, a long-time antitrust hawk, that prospect raises significant concerns about dominant market power.

"Will Universal's music catalog be so large as to make it a gatekeeper that can make or break any new online service and allow it to prevent new competitively priced services from launching?" Kohl challenged. "In almost all industries, reducing the number of competitors from four to three expands the market power of the remaining companies and increases the risk of higher prices. Why shouldn't these same principles apply to the music business?"

Some opponents of the transaction see a parallel with AT&T's . The wireless market is similarly dominated by four major players, thus raising concerns of undue market concentration when one proposes to acquire another.