In a letter Monday to Assistant Attorney General Christine Varney, Sen. Herb Kohl, D-Wis., called on the Justice Department to approve the transaction only if it will not harm competition and will not lead to higher prices for consumers. As chairman of Senate Judiciary Committee’s antitrust subcommittee, Kohl holds sway with the agency.

In a separate letter to Varney on Monday, 50 House members said the Justice Department should examine the merger “with great skepticism” because the combined company “would enjoy a virtual stranglehold over the live entertainment industry.”

Ticketmaster and Live Nation have been seeking to allay antitrust concerns among lawmakers and regulators in Washington since they announced their proposed merger in February.

Ticketmaster, based in West Hollywood, Calif., is the nation’s largest seller of tickets to live concerts and other entertainment events. It also owns an artist management company, Front Line Management, and a ticket-reselling company called

Live Nation, based in Los Angeles, is the country’s largest concert producer. It also owns entertainment venues and in January launched its own ticket-selling business, which currently competes with Ticketmaster.

The loss of this competition, Kohl warned, could lead to higher ticket prices for consumers.

He added that the merger will create “an enormous, vertically integrated entertainment giant” that controls everything from artist management, concert promotion, concert venues and merchandise sales to primary and secondary market ticket sales. That, he said, would make it difficult for smaller competitors or new entrants to gain a foothold in the market.

Kohl also said the merged company could “effectively choke off” the secondary market for ticket resales.

Some of those same concerns were echoed in a letter written by Rep. William Pascrell Jr., D-N.J., and signed by 50 House members. “There are few artists, promoters, venue owners, or concertgoers that would not feel the impact of this merger,” the letter stated. “In our view, the merger should be prohibited.”

Pascrell has also called for a federal investigation of Ticketmaster after Bruce Springsteen fans who attempted to buy tickets to concerts in New Jersey through in February were redirected to the company’s Web site, which was selling the tickets at higher prices. Ticketmaster blamed the problem on a software glitch.

Gina Talamona, a spokeswoman for the Justice Department, said only that the agency is conducting an active, ongoing investigation of the merger. Live Nation had no comment. And Ticketmaster did not respond to a request for comment.