“We are committed to going to court to block those mergers that will substantially reduce competition,” Varney said, according to prepared remarks. “The commitment to litigate enhances our ability to negotiate settlements that simultaneously enable any pro-competitive aspects of a deal to go forward yet also prevent harm to consumers.”

The Justice Department approved a merger between ticket giant Ticketmaster and concert promoter Live Nation earlier this year, for example, only after the firm agreed to spin off one ticketing unit, license some of its software, and refrain from a host of practices the DOJ determined could be anti-competitive.

The Antitrust Division also sued dairy giant Dean Foods in January, seeking to undo its 2009 purchase of some milk processing plants in Wisconsin. That deal was not subject to antitrust scrutiny before it closed because it did not meet the size threshold for a regulatory review.

“[W]e are doing all we can to ensure that our markets are open and fair,” Varney said at today’s oversight hearing, which was held in front of the House Judiciary courts and competition subcommittee.

Committee Chairman John Conyers (D-Mich.), who said anti-competitive practices are “roaring down the runway,” argued that antitrust issues have grown more technical and complex.

“Antitrust enforcement is critical to the capitalist system,” Conyers said. “Free and competitive markets are the foundation of an economy like ours. When the markets fail, the economy fails.”

Lamar Smith of Texas, the ranking Republican on the committee, said he supports the strong defense of antitrust laws, but called on antitrust leaders to be transparent and reasonable on enforcement.

“American businesses need to have clear rules of the road in order to compete effectively against each other and in world markets,” Smith said.

Additional reporting by Aruna Viswanatha.